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/.mcp.json

@@ -1,11 +0,0 @@
-{
-  "mcpServers": {
-    "agenthub": {
-      "command": "node",
-      "args": ["${CLAUDE_PLUGIN_ROOT}/mcp/build/index.js"],
-      "env": {
-        "AGENTHUB_DASHBOARD_URL": "http://localhost:4820"
-      }
-    }
-  }
-}

plugins/agenthub/commands/agenthub-doctor.md

@@ -1,5 +1,5 @@
 ---
-description: Diagnose a plugin-installed AgentHub — Node, bootstrap, server, hooks, CLI, MCP build
+description: Diagnose a plugin-installed AgentHub — Node, bootstrap, server, hooks, CLI
 ---
 
 Run the diagnostic and report what it found. Do not fix anything unless the user
@@ -18,9 +18,7 @@ Print the output verbatim, then add at most three lines of guidance based on the
   Starting a new Claude Code session removes them automatically (the bootstrap
   backs the file up as `settings.json.agenthub-bak` first).
 - `FAIL Server` or `FAIL Runtime deps` → run `/agenthub-update`, then check
-  `~/.claude/agent-dashboard/runtime/bootstrap.log` and `server.log`.
-- `FAIL MCP build` → `mcp/build/` is out of date; run `npm run mcp:build` in a
-  checkout and commit it.
+  `~/.claude/agenthub/runtime/bootstrap.log` and `server.log`.
 - `WARN agenthub CLI` → print the exact `export PATH=...` line from the output.
 - `WARN Skill plugins` → the pipelines name slash commands no installed plugin
   provides. The dashboard is unaffected; `/agenthub:ship-feature(-lane)` is what

plugins/agenthub/commands/agenthub-open.md

@@ -5,7 +5,7 @@ description: Rebuild the dashboard UI and print its URL
 Rebuild the dashboard bundle, then print the URL. Always forces a rebuild so a
 stale bundle (e.g. after a fix commit landed but the bootstrap's build predates
 it) never serves silently. Also finishes the build if the bootstrap's own
-attempt failed (check `~/.claude/agent-dashboard/runtime/client-build.log`).
+attempt failed (check `~/.claude/agenthub/runtime/client-build.log`).
 
 ```bash
 node "${CLAUDE_PLUGIN_ROOT}/scripts/plugin-open.js" --force

plugins/agenthub/commands/agenthub-update.md

@@ -46,4 +46,4 @@ node "${CLAUDE_PLUGIN_ROOT}/scripts/plugin-doctor.js"
 ```
 
 Report the final state in a few lines. If the bootstrap failed, quote the
-decisive line from `~/.claude/agent-dashboard/runtime/bootstrap.log`.
+decisive line from `~/.claude/agenthub/runtime/bootstrap.log`.