fix(scan report): render readable text

[John-David Dalton (jdalton)]

LLM Description written by Codex:GPT-6

Summary

Render the default socket scan report output as readable plain text for terminal and CI logs. Keep JSON, Markdown, short output, error handling, and exit status behavior intact. Share alert flattening between plain text and Markdown renderers.

Validation

• Before the large-report regression was added, the focused unit file passed all 9 cases when run as SOCKET_SHIM_ACTIVE_PNPM=1 pnpm run test:unit src/commands/scan/output-scan-report-text.test.mts. This prefix bypassed the managed wrapper's token and SFW launcher. The normal wrapper rejected its configured token, so I have not rerun locally. CI is pending for the 200,000-alert regression.
• CI lint identified no-control-regex in the original ANSI check. The check now uses a string/codepoint test; CI must verify the fix.
• git diff --check passed.
• pnpm run check:tsc:src reported an unrelated existing error at src/commands/optimize/update-manifest-by-agent.mts:140: EditablePackageJson.fromJSON is missing.