[codex] simplify wordpress compose

[henmohr]

What changed

• Replaced the root-level WordPress override with a self-contained Compose file.

• Switched the local WordPress password default to admin.

• Updated the root README and Makefile to use the new root compose entrypoint.

• Bumped the wordpress-docker submodule pointer to the published documentation change.

Why

• Running docker compose -f docker-compose.override.yml up from the repository root previously failed because the override depended on a relative common-services.yml file inside the submodule.
• The root workflow now works from the repository root without manual path adjustments.

Impact

• make up and make down now target the same root compose file that docker compose -f docker-compose.override.yml uses.

• The local WordPress password reset flow is aligned to the existing admlibrecode account with password admin.

Validation

• Ran docker compose -f docker-compose.override.yml config successfully.

• Verified the running WordPress users and reset the local admlibrecode account during testing.