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.

plugins/agenthub-devtools/agents/issue-triager.md

@@ -4,8 +4,8 @@ description: >
   Triages Agent Monitor issues by systematically checking the Express API
   (port 4820), SQLite database (better-sqlite3 with WAL mode), WebSocket
   broadcast, hook handler (scripts/hook-handler.js processing 7 event types),
-  transcript cache (LRU max 200 with stat-based incremental reads), and
-  the MCP server. Classifies by severity and provides specific remediation.
+  and transcript cache (LRU max 200 with stat-based incremental reads).
+  Classifies by severity and provides specific remediation.
 model: sonnet
 tools:
   - Bash
@@ -28,7 +28,6 @@ The Agent Monitor has these components:
 - **Hook Handler** (`scripts/hook-handler.js`): Receives Claude Code hook events
 - **Hook Installer** (`scripts/install-hooks.js`): Configures hooks in `~/.claude/settings.json`
 - **Client** (`client/`): React + Vite SPA on port 5173 (dev) or served by Express (prod)
-- **MCP Server** (`mcp/`): Model Context Protocol integration
 
 ## Investigation Process
 
@@ -78,7 +77,7 @@ For each triaged issue, provide:
 ┌─────────────────────────────────────────┐
 │ Issue: [Brief title]                     │
 │ Severity: P[0-3] [Critical/High/Med/Low] │
-│ Component: [server/client/hooks/db/mcp]  │
+│ Component: [server/client/hooks/db]      │
 │ Status: [investigating/identified/fixed]  │
 └─────────────────────────────────────────┘