docs: the Project plugin is missing from the root READMEs and the two index pages #2842

Written-by: Chief

Owner: Dev
Reviewer: Reviewer

plugins/project (@flybot/project) landed in #2829 and packs correctly after #2841, but the three index pages that tell a reader what ships still describe five plugins. Nothing is broken at runtime; a reader installing from the README or browsing docs/ has no way to learn the Project domain exists.

Where the gap is

1. README.md — "Also in the app" lists Task board, group chats, Workflows (@flybot/workflow), Schedules, Connectors, Timeline (@flybot/timeline) — no Project entry. The plugin is already named in the install line (line ~114) and the Docs list (line ~157), so the page contradicts itself: it tells you to add path:/plugins/project and never says what you get.
2. README.zh.md — same section (line ~101 install line, ~143 Docs list), same missing entry.
3. docs/architecture.md:12-15 — the plugin table has rows for plugins/social/, plugins/tree/, plugins/timeline/, plugins/workflow/ and no plugins/project/.
4. docs/subsystems/README.md — the index table lists tree, timeline, workflow, social and no project, although docs/subsystems/project.md exists and carries owned_paths: plugins/project/.

What to write

One bullet in each README (Chinese in the zh file), two or three lines, in the voice of the neighbouring bullets: a Project is Project State (a file the day's work is recorded in), its board of cards by column, its own Chief that runs the day, the team dossier and the metrics page, and an assistant that answers from the Project's own records; the core keeps the Project record and the project-* endpoints, the domain lives in the plugin, and the switch is in Settings like the other plugins. Do not claim anything the code does not do — read plugins/project/README.md and docs/subsystems/project.md first and describe what they describe.

The two table rows are one line each: | \plugins/project/` | `@flybot/project` — the Project domain: Project State, board, Project Chief, team dossier, metrics, assistant. |and| project | project.md | `plugins/project/` |` in the same position the other plugins take.

Acceptance

• grep -c 'plugins/project' README.md README.zh.md docs/architecture.md docs/subsystems/README.md is non-zero for all four, and the README bullet renders in the same list style as its neighbours (no new heading).
• node core/scripts/check-arch-docs.mjs stays green (npm --prefix core run lint if that is what wraps it).
• No file under policy/ or .github/workflows/ is touched, so this needs no Policy-sign:.
• Docs only: no code, no test change. If a line in plugins/project/README.md and docs/subsystems/project.md disagrees with what you would write, say so in the PR body instead of quietly picking one.