Introduce new blog contribution skill and references

.agents/skills/contribute-blog/SKILL.md

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+---
+name: contribute-blog
+description: >-
+  Create, import, edit, or review posts for the
+  official Flutter blog at flutter.dev/blog,
+  including metadata, media, authors, and publication checks.
+---
+
+# Contribute to the Flutter blog
+
+## Editorial approach
+
+Preserve the author's voice, intent, and requested scope.
+First person, contractions, anecdotes, humor, enthusiasm,
+and future-facing announcements can all be appropriate.
+Don't rewrite them merely to match documentation conventions.
+
+Apply `write-technical-docs` and `format-markdown` selectively for clarity,
+accuracy, accessibility, links, code formatting, and sound structure.
+Their documentation-specific preferences aren't blanket blog requirements:
+semantic line breaks and an 80-character limit aren't required,
+especially when importing or lightly editing an existing post.
+
+Fix or flag substantive issues with source fidelity,
+technical accuracy, accessibility, metadata, or rendering.
+Treat preference-only rewrites as suggestions
+unless copyediting was requested.
+
+## Read relevant reference material
+
+- For a new post, import, metadata or media change,
+  structural edit, or full review, read
+  [Flutter blog post format](references/post-format.md).
+- For a Google Doc import, also read
+  [Import from Google Docs](references/google-doc-import.md).
+- To add or update an author or resolve an unknown author ID, read
+  [Manage blog authors](references/authors.md).
+
+A small prose-only correction might need no reference.
+Consult `sites/www/content/blog/data.yaml`,
+`sites/www/content/blog/authors.yaml`, comparable recent posts,
+or implementation source when a convention is unclear.
+
+## Code and quality checks
+
+- If changing or writing Dart or Flutter samples,
+  apply `write-dart` and `write-flutter` as relevant.
+  Validate complete examples when practical and
+  label intentional omissions or pseudocode clearly.
+- Before calling a post ready,
+  search the changed content for unresolved markers and placeholders,
+  such as `TODO`, `TBD`, or placeholder notes.
+  Report intentional markers or blockers instead of silently removing them.
+
+## Validate proportionally
+
+For a new post or a change to metadata or content,
+run the build and link-reference checks:
+
+```bash
+dart run dash_site --site=www build
+dart run dash_site --site=www check-link-references
+```
+
+When layout, media, metadata, or content significantly changes,
+consider previewing the site locally:
+
+```bash
+dart run dash_site --site=www serve
+```
+
+For a prose-only edit that doesn't change links,
+direct inspection of the content can be enough.

.agents/skills/contribute-blog/references/authors.md

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+# Manage blog authors
+
+Use this reference when adding or updating an author,
+or when a post's author ID doesn't resolve.
+
+Authors are defined in `sites/www/content/blog/authors.yaml`, and
+their local profile images live in `sites/www/content/blog/author_images/`.
+
+The top-level key in `authors.yaml` is a stable content ID,
+not necessarily the author's current social handle.
+
+## Add or resolve an author
+
+Before adding a record,
+search `authors.yaml` by ID, display name, and profile URL.
+Use verified or author-provided details.
+Don't invent a name, profile, or image.
+For a new ID, choose a recognizable lowercase handle or concise stable slug,
+then insert the record alphabetically by ID.
+
+`name` is required while `image`, `imageUrl`, and `link` are optional:
+
+```yaml
+author-id:
+  name: "Author Display Name"
+  image: "author-id.webp"
+  link: "https://github.com/author-id"
+```
+
+- `image` names a local image file in `author_images/`.
+- `imageUrl` accepts an external URL to use as a fallback to `image`.
+  Prefer a local `image` over setting `imageUrl`. Don't set both.
+- `link` is the destination linked from the byline. Prefer their GitHub profile.
+
+## Author images
+
+Name a local image after the exact author ID and
+use its real lowercase `.jpg` or `.webp` extension,
+such as `author-id.webp`.
+Optimize it for a small square display and a centered circular crop.
+Use an author-supplied or appropriately reusable image.
+
+## Update an author
+
+Keep the existing ID when an author's name, handle, link, or image changes.
+If the ID must change, update every occurrence in post frontmatter.
+
+When replacing an image with a different filename or extension,
+search for references to the old file before removing it.
+Don't remove an apparently unused author without checking all posts.
+
+## Configure the authors of a post
+
+In a post's `index.md` frontmatter:
+
+For a single author, use a YAML scalar:
+
+```yaml
+author: author-id
+```
+
+For multiple authors, use an ordered list:
+
+```yaml
+author:
+  - first-author
+  - second-author
+```
+
+List order controls the displayed byline.

.agents/skills/contribute-blog/references/google-doc-import.md

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+# Import from Google Docs
+
+Use this reference to convert an authored Google Doc into a Flutter blog post
+without turning the import into an unsolicited rewrite.
+
+## Get the source
+
+First, try to download the source yourself.
+Open the document in an authenticated browser and choose
+**File > Download > Web Page (.html, zipped)**.
+An authenticated Google Docs or Drive connector is also suitable
+if it can produce the complete HTML export and original media.
+
+If you can't access the document, the download fails,
+or the export is incomplete,
+ask the user to download and provide the HTML zip.
+Don't reconstruct content that the available source omits.
+
+Import the document body as exported.
+Ignore comment threads and suggestion metadata,
+don't reproduce or act on them.
+Extract exports into a temporary directory and
+don't commit the source archive or intermediate conversion files.
+
+## Convert content, not export debris
+
+Preserve the document's structure and meaning,
+including headings, prose, lists, tables, emphasis, links,
+code, images, and captions.
+Convert ordinary content to clean Markdown,
+using site components when they provide necessary behavior.
+
+Strip Google Docs export artifacts:
+
+- **Redirects**:
+  Replace Google redirect and tracking URLs with their direct destinations.
+- **Styling spans & non-breaking spaces**:
+  Remove non-relevant markup and structure, such as
+  inline CSS, font declarations, classes, empty anchors, and wrapping spans.
+- Replace ` ` with standard whitespace.
+- **Code snippets**:
+  Convert exported code to fenced Markdown blocks
+  with appropriate language identifiers, such as `dart` or `bash`.
+  Google Docs might represent code as `<p>` tags with
+  `&nbsp;` indentation or as single-cell tables.
+- **Titles**:
+  Don't replicate the document title as an `# H1` heading in the Markdown body.
+  The `title` in the post's frontmatter supplies the page H1.
+- **Footnotes**:
+  Preserve footnote content,
+  but omit generated Google Docs anchor navigation links.
+- **Videos**: Convert standalone YouTube links into `<YouTubeEmbed>` components.
+
+Keep the author's person, tone, pacing, spelling variety,
+heading style, and rhetorical choices unless editing was requested.
+Correct conversion errors,
+but surface optional prose changes separately.
+
+## Resolve authors
+
+Identify the ordered authors from an explicit byline or user context,
+not from document ownership or editor metadata.
+
+To resolve their IDs and configure the post's frontmatter,
+follow the steps in [Manage blog authors](authors.md).
+If the source lacks enough information to identify or resolve an author,
+ask the user for their GitHub or other profile URL.
+
+## Reconcile images
+
+Map each exported image to
+its source position, caption, and purpose
+before renaming or moving it:
+
+- Place images in the post's `images/` directory
+  with concise, descriptive names.
+- Keep the highest-quality intended source.
+  Convert static raster images to WebP when quality and clarity are preserved.
+- If the image is a JPEG, prefer a `.jpg` extension over `.jpeg`.
+- Preserve intentional animation
+  and provide a static `socialImage` when needed.
+- Follow the alt text and `<DashImage>` guidance in
+  [Flutter blog post format](post-format.md).
+- If an image's purpose or placement is ambiguous,
+  ask for guidance rather than guessing.
+
+## Check fidelity
+
+Compare the converted post with the source section by section.
+Confirm that no prose, list item, code block, table row, image, caption,
+footnote, or intended link is missing or misplaced.
+Check heading hierarchy, link destinations, image-caption pairings,
+and meaningful emphasis.
+Report any placeholder or editorial hold in the document body
+that prevents the post from being ready.
+
+Finish with the format and accessibility checks in
+[Flutter blog post format](post-format.md)
+and the validation workflow in the [parent skill](../SKILL.md).