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.

Makefile

@@ -10,7 +10,6 @@
 #   make start            # Start the production server
 #   make test             # Run all tests
 #   make format           # Format all files with Prettier
-#   make mcp-dev          # Start MCP server in watch mode
 #   make seed             # Load deterministic demo data
 # For more commands, run `make help` to see descriptions, or see below.
 # ─────────────────────────────────────────────────────────────────────────────
@@ -21,10 +20,9 @@ SHELL         := /bin/bash
 # ─── Setup ──────────────────────────────────────────────────────────────────
 
 .PHONY: setup
-setup: ## Install all dependencies (root + client + MCP)
+setup: ## Install all dependencies (root + client)
 	npm install
 	cd client && npm install
-	npm --prefix mcp install
 
 .PHONY: install-hooks
 install-hooks: ## Register Claude Code hooks in ~/.claude/settings.json
@@ -82,28 +80,6 @@ format: ## Format all files with Prettier
 format-check: ## Check formatting without writing
 	npx prettier --check .
 
-# ─── MCP Server ─────────────────────────────────────────────────────────────
-
-.PHONY: mcp-install
-mcp-install: ## Install MCP server dependencies
-	npm --prefix mcp install
-
-.PHONY: mcp-build
-mcp-build: ## Compile MCP TypeScript → JavaScript
-	npm --prefix mcp run build
-
-.PHONY: mcp-typecheck
-mcp-typecheck: ## Type-check MCP source without emitting
-	npm --prefix mcp run typecheck
-
-.PHONY: mcp-start
-mcp-start: ## Start the MCP stdio server
-	npm --prefix mcp run start
-
-.PHONY: mcp-dev
-mcp-dev: ## Start MCP server in watch mode
-	npm --prefix mcp run dev
-
 # ─── Data Management ───────────────────────────────────────────────────────
 
 .PHONY: seed
@@ -136,17 +112,11 @@ docker-down: ## Stop docker-compose stack
 docker-logs: ## Tail docker-compose logs
 	docker compose logs -f
 
-.PHONY: mcp-docker-build
-mcp-docker-build: ## Build MCP Docker image
-	docker build -f mcp/Dockerfile -t agent-dashboard-mcp:local .
 
 .PHONY: podman-build
 podman-build: ## Build dashboard Podman image
 	podman build -t localhost/claude-agent-monitor:local .
 
-.PHONY: mcp-podman-build
-mcp-podman-build: ## Build MCP Podman image
-	podman build -f mcp/Dockerfile -t localhost/agent-dashboard-mcp:local .
 
 # ─── Help ───────────────────────────────────────────────────────────────────