ASH-49: add project Context view

[Asherggg]

Summary

• Add the project-page Context peer view with search, kind/tag/pinned/archive filters, cursor pagination, inline detail/edit, revisions, pin/archive/restore, and responsive list/detail navigation.
• Consume the ASH-46 client contract and wire Context events/revision polling into the existing shell.
• Preserve editor drafts across VERSION_CONFLICT by fetching the latest entry and retrying with the refreshed version; render Markdown through react-markdown without raw HTML.

Dependency

This branch is based on the ASH-45/ASH-46 API commits currently in PR #17. It is intentionally opened against main so the dependency commits remain visible until that PR lands.

Verification

• npm run typecheck
• npm run build
• node --test test/context-ui.test.mjs test/board-views.test.mjs (15/15)
• npm run check (344/362 overall; 18 pre-existing failures outside Context)
• Playwright desktop and 720px browser checks: no horizontal overflow; safe Markdown produced no executable script/onerror nodes; create/search/revisions/409 draft preservation/archive/restore passed; cursor pagination appended 53 unique rows.

No production deployment is included.