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.

.codex/skills/repo-onboarding/SKILL.md

@@ -7,14 +7,13 @@ description: Understand this repository quickly before making changes. Use for a
 
 ## Workflow
 - Read `AGENTS.md`, `README.md`, and `ARCHITECTURE.md`.
-- Determine target layer: `server/`, `client/`, `mcp/`, or docs.
+- Determine target layer: `server/`, `client/`, or docs.
 - Identify the minimal file set needed for the task.
 - Select verification commands before editing.
 
 ## Verification defaults
 - Backend: `npm run test:server`
 - Frontend: `npm run test:client`
-- MCP: `npm run mcp:typecheck` and `npm run mcp:build`
 
 ## References
 - `references/module-map.md`

.codex/skills/repo-onboarding/references/module-map.md

@@ -6,4 +6,3 @@
 - `server/websocket.js`: live update broadcast path.
 - `client/src/pages/`: route-level UI.
 - `client/src/components/`: reusable UI primitives.
-- `mcp/src/tools/domains/`: MCP tool families.

.codex/skills/repo-onboarding/references/verification-map.md

@@ -4,8 +4,5 @@
   - `npm run test:server`
 - Frontend changes:
   - `npm run test:client`
-- MCP changes:
-  - `npm run mcp:typecheck`
-  - `npm run mcp:build`
 - Docs-only changes:
   - validate command consistency against root `package.json`