refactor: finish the AgentHub rename and drop the MCP server

Two leftovers from the rebrand, done together because they touch the same
docs and manifests.

**Data directory.** `agent-dashboard` could not simply be renamed in the
source: it names a real directory holding the live SQLite database. Startup
now moves it once, via `migrateLegacyDataDir()` in `server/lib/claude-home.js`
— a same-filesystem rename, so it is instant even at multiple gigabytes and
cannot leave two divergent copies. `getDataDir()` stays PURE and resolves to
the legacy path until the move happens; the first version of this put the
rename inside the getter, which meant `npm run test:server` relocated the
developer's real database as a side effect. The call sits behind
`require.main === module` and ahead of the router requires, because those pull
in db.js, which opens SQLite at module load. A failed rename is silent and the
old directory keeps being used: an unfashionable directory name beats a blank
database beside an unreachable one. Same treatment for the port-discovery file
(`.agent-dashboard.json` → `.agenthub.json`, old one dropped on write).

Not renamed on purpose: the Sagi localStorage keys (renaming silently resets
everyone's prefs) and the PWA manifest `id` (changing it orphans an installed
app).

**MCP server.** 4 tool calls in 46 days across 577,132 events, against 4,556
lines of TypeScript, a 2 MB committed build artifact, and a pre-commit guard
that had already blocked commits twice. Deleted: `mcp/`, the maintainer skills
and `mcp-reviewer` agent, the build check, `plugins/agenthub/.mcp.json`,
`docs/MCP.md`, 12 npm scripts, 5 Makefile targets, and every doc section
describing it.

Kept, because they are unrelated things sharing the name: the Config
Explorer's MCP tab and its API, per-lane Playwright MCP, the agenthub-config
plugin's MCP audit, and the historical `mcp__plugin_agenthub_*` events that
analytics must keep attributing.

Verified: server 1432/1432, client 459/459, tsc clean, prettier clean. Both
directions of the migration proven — a sandbox-HOME test run leaves the legacy
directory untouched, and a real boot moves it with its contents intact.

README.vi.md

@@ -27,8 +27,7 @@ Internal build — all rights reserved.
   thật, render bằng xterm.js) gắn vào thư mục của lane — đúng cái TUI bạn thấy ở
   máy, tương tác đầy đủ, resume được, và attach được từ terminal thật qua
   `agenthub lanes shell`. Chạy CLI nào là thiết lập riêng của từng lane.
-- **Analytics (tab trong dashboard), alert và workflow view**, cộng thêm MCP
-  server và CLI.
+- **Analytics (tab trong dashboard), alert và workflow view**, cộng thêm CLI.
 
 ## Yêu cầu
 
@@ -47,7 +46,7 @@ Hai lệnh, trên máy chỉ có Claude Code, không cần clone repo, không c
 ```
 
 Lần session-start đầu tiên sẽ cài hooks, boot server, đưa `agenthub` vào PATH và
-kết nối MCP tools; chạy detached nên session không phải chờ. `/agenthub-doctor`
+chạy detached nên session không phải chờ. `/agenthub-doctor`
 báo trạng thái, `/agenthub-open` build UI và in URL, `/agenthub-update` refresh sau
 khi plugin update. Đường này cần Node **>= 22.5** (không dùng
 `better-sqlite3` native, server dùng `node:sqlite`). Chi tiết, kể cả những gì
@@ -190,7 +189,6 @@ thêm Prettier.
 | `server/` | Express API, schema SQLite, hook ingest, thư viện lane và worktree |
 | `client/` | Dashboard React 18 + Vite + Tailwind |
 | `bin/agenthub.js` | CLI |
-| `mcp/` | MCP server expose các tool đọc dữ liệu dashboard (read-only) |
 | `docs/` | Architecture, API, lanes, database |
 | `plugins/` | Các Claude Code plugin đi kèm dashboard |