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.

skills/ship-feature/SKILL.md

@@ -43,7 +43,7 @@ you dropped back to.
 - `agenthub stage intake --status running`
 - Restate the requirement and its success criteria.
 - Explore the impacted modules: `Explore` agent for breadth, then read the key
-  files yourself. Identify which layers are hit (server / client / mcp / docs /
+  files yourself. Identify which layers are hit (server / client / docs /
   scripts) — `repo-onboarding` if the area is unfamiliar.
 - Requirement fuzzy or open to more than one reading? **superpowers:brainstorming**.
 
@@ -79,7 +79,7 @@ you dropped back to.
     weaken existing tests. Final line: `UNIT-TESTS: PASS — <n> added` or
     `UNIT-TESTS: FAIL — <test> :: <defect>`.
   - **Suite run.** Backend changed → `npm run test:server`. Frontend →
-    `npm run test:client`. MCP → `npm run mcp:typecheck` + `npm run mcp:build`.
+    `npm run test:client`.
     A UI snapshot diff is reported for review, **never blindly regenerated**
     (`cd client && npx vitest run -u` is yours to run, only after you read the
     diff).
@@ -101,15 +101,14 @@ you dropped back to.
   Agent calls).** Check `git diff --name-only` (against the base this task
   started from) for touched layers and launch every matching one —
   FOREGROUND, fresh context, never `fork`, addressed as `agenthub:backend-reviewer`
-  / `agenthub:frontend-reviewer` / `agenthub:mcp-reviewer`:
+  / `agenthub:frontend-reviewer`:
   - Any path under `server/` → `agenthub:backend-reviewer`.
   - Any path under `client/` → `agenthub:frontend-reviewer`.
-  - Any path under `mcp/` → `agenthub:mcp-reviewer`.
-  - None of those three touched → skip all three; the generic Code Reviewer
+  - Neither touched → skip both; the generic Code Reviewer
     above is the only gate.
   - Hand each ONLY the repo path and the working diff — each scopes itself to
     its own domain's files. Each ends with its own parseable line:
-    `BACKEND-REVIEW:` / `FRONTEND-REVIEW:` / `MCP-REVIEW:` — `CLEAN` or
+    `BACKEND-REVIEW:` / `FRONTEND-REVIEW:` — `CLEAN` or
     `FINDINGS — <n>`.
 - Apply what is worth applying — the generic review plus every domain
   reviewer that ran — with **superpowers:receiving-code-review** judgment:

skills/ship-feature/references/feature-checklist.md

@@ -2,7 +2,7 @@
 
 - Scope
   - Problem and success criteria are explicit.
-  - Impacted layers identified (server/client/mcp/docs/scripts).
+  - Impacted layers identified (server/client/docs/scripts).
 
 - Implementation
   - Input validation and error handling are explicit.
@@ -12,10 +12,9 @@
 - Verification
   - Backend: `npm run test:server` when backend changed.
   - Frontend: `npm run test:client` when UI changed.
-  - MCP: `npm run mcp:typecheck` + `npm run mcp:build` when MCP changed.
 
 - Documentation
-  - `README.md`, `ARCHITECTURE.md`, `SETUP.md`, `INSTALL.md`, `mcp/README.md` updated as needed.
+  - `README.md`, `ARCHITECTURE.md`, `SETUP.md`, `INSTALL.md` updated as needed.
   - Commands in docs match `package.json`.
 
 - Delivery