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.md

@@ -27,7 +27,7 @@ Internal build — all rights reserved.
   you'd see locally, fully interactive, resumable, and attachable from a real
   terminal too via `agenthub lanes shell`. Which CLI it starts is the lane's own
   setting.
-- **Analytics (in-dashboard tab), alerts, and a workflow view**, plus an MCP server and a CLI.
+- **Analytics (in-dashboard tab), alerts, and a workflow view**, plus a CLI.
 
 ## Requirements
 
@@ -41,7 +41,7 @@ by the dashboard. `/agenthub:ship-feature` and `/agenthub:ship-feature-lane` dri
 `superpowers:brainstorming`, `writing-plans`, `test-driven-development`,
 `requesting-code-review` and `verification-before-completion` phase by phase,
 and both built-in pipeline templates name those same slash commands as their
-per-node drivers. Without it the dashboard, hooks, CLI and MCP all work
+per-node drivers. Without it the dashboard, hooks and CLI all work
 normally — the two pipeline skills are what stop partway. `/agenthub-doctor` reports
 it as a `WARN` row.
 
@@ -49,7 +49,7 @@ it as a `WARN` row.
 bootstrap installs it for you, once, in its detached worker — so a session never
 waits on the clone, and the current session needs `/reload-plugins` before the
 skills resolve (any later session picks them up on its own). The outcome is
-logged to `~/.claude/agent-dashboard/runtime/bootstrap.log`, and `/agenthub-update`
+logged to `~/.claude/agenthub/runtime/bootstrap.log`, and `/agenthub-update`
 retries a failed one. To install it by hand instead, or after opting out:
 
 ```bash
@@ -73,7 +73,7 @@ Two commands on a machine that has nothing but Claude Code, no clone and no
 ```
 
 The first session start installs the hooks, boots the server, puts `agenthub` on
-PATH and connects the MCP tools; it runs detached, so the session never waits on
+PATH; it runs detached, so the session never waits on
 it. `/agenthub-doctor` reports the state, `/agenthub-open` builds the UI and prints the
 URL, `/agenthub-update` refreshes after a plugin update. This path needs Node
 **>= 22.5** (no native `better-sqlite3`, so the server uses `node:sqlite`).
@@ -224,7 +224,6 @@ Both must be green before a commit; the pre-commit hook runs them plus Prettier.
 | `server/` | Express API, SQLite schema, hook ingest, lane and worktree libraries |
 | `client/` | React 18 + Vite + Tailwind dashboard |
 | `bin/agenthub.js` | CLI |
-| `mcp/` | MCP server exposing read-only dashboard tools |
 | `docs/` | Architecture, API, lanes, database |
 | `plugins/` | Claude Code plugins shipped with the dashboard |