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.

scripts/plugin-doctor.js

@@ -4,8 +4,7 @@
  * @description Reports the health of a plugin-installed AgentHub: Node version,
  * bootstrap state, runtime dependencies, server liveness, duplicate hook
  * entries (the one failure that silently doubles every token and cost figure),
- * the `agenthub` CLI launcher and its PATH, whether the committed MCP build still
- * matches `mcp/src`, and whether the slash commands the pipeline templates name
+ * the `agenthub` CLI launcher and its PATH, and whether the slash commands the pipeline templates name
  * as node drivers are actually resolvable (the `superpowers` plugin, today).
  * Read-only — it diagnoses, it never repairs.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
@@ -17,7 +16,6 @@ const path = require("path");
 
 const boot = require("./plugin-bootstrap");
 const { getSettingsPath, getDataDir } = require("../server/lib/claude-home");
-const { mcpBuildStatus } = require("./check-mcp-build");
 
 const PLUGIN_ROOT = path.resolve(__dirname, "..");
 
@@ -85,13 +83,6 @@ function diagnose() {
   add(...cliStatus());
   add(...skillPluginStatus());
 
-  const mcp = mcpBuildStatus(PLUGIN_ROOT);
-  add(
-    mcp.ok ? "ok" : "fail",
-    "MCP build",
-    mcp.ok ? "matches mcp/src" : `${mcp.reason} — run npm run mcp:build`
-  );
-
   const dist = process.env.DASHBOARD_CLIENT_DIST || path.join(rt, "client-dist");
   add(
     fs.existsSync(path.join(dist, "index.html")) ? "ok" : "warn",
@@ -104,7 +95,7 @@ function diagnose() {
 
 /**
  * WARN (never FAIL) when a plugin the pipelines depend on cannot be resolved:
- * the dashboard, hooks, CLI and MCP all work without it — only the pipeline
+ * the dashboard, hooks and CLI all work without it — only the pipeline
  * skills that drive it stop partway, so this must not fail a doctor run.
  *
  * The requirement derivation and the missing/satisfied rules live in