[EndlessCCL]

What this PR does

Improve Help Center search with progressive keyword retrieval, optional semantic search and bilingual query fallback. Improve Agent article retrieval and citation grounding.

Add durable indexing for published articles. Unpublishing retains but disables indexes; republishing rebuilds them. Allow unchanged saves to trigger missing indexes or retry failures. Include migration 0020_help_vector_index, with no historical article backfill.

Preserve existing publication and AI visibility badges. Show indexing and failure indicators in article lists; show not-indexed, indexing and failed states in the editor. Expand the editor responsively within bounded dimensions.

Why

Readers and the Agent need to find relevant article content beyond exact keyword matches. Authors need clear indexing feedback and a way to retry failures without modifying their articles.

How to review

• Start with server/lib/help-search, the Help Center services and search API.
• Verify keyword search with semantic search disabled, then enable it and test hybrid retrieval.
• Publish, unpublish and republish an article; confirm only published articles participate in advanced search.
• Save an unindexed or failed article without editing its content to trigger indexing.
• Verify list indicators, editor status visibility and responsive editor sizing.
• Confirm draft AI visibility still follows the existing AI usage setting.
• Review 0020_help_vector_index: existing migrations remain unchanged, with no historical article backfill. No content-hash field is added.

Relevant indexing and Agent search tests, changed-file lint checks and the Docker application build passed. Full lint still reports existing errors.

Checklist

• Commits are signed off (git commit -s)
• Tests pass locally (pnpm build)
• If schema changed, migration was generated and committed
• Public environment options are documented in .env.example
• No secrets, internal URLs, or team member names in the diff