feat(plugins): make CCAM installable straight from a Claude Code plugin

Adds a root `ccam` plugin (`.claude-plugin/plugin.json`, `"source": "./"`) so
`/plugin marketplace add` + `/plugin install ccam@...` is enough on a machine
with nothing but Claude Code: no clone, no npm run setup, no manual npm start.

- scripts/plugin-bootstrap.js: SessionStart hook. Fast-path exit, Node >=22.5
  gate (node:sqlite), mkdir lock with stale reclaim, deps installed into
  ~/.claude/agent-dashboard/runtime/ (never the plugin cache), legacy
  checkout-hook cleanup (backed up), ~/.local/bin/ccam launcher, eager UI
  build so client routes like /run work immediately, detached server spawn.
- scripts/plugin-open.js, scripts/plugin-doctor.js: /ccam-open, /ccam-doctor.
- server/index.js: DASHBOARD_CLIENT_DIST override (plugin cache is read-only).
- mcp/build/ is committed (plugin MCP servers start before any bootstrap could
  build them) and kept honest by scripts/check-mcp-build.js (content hash,
  not mtime), enforced by pre-commit when mcp/src changes.
- plugins/ccam-dashboard/.mcp.json moved under plugins/ccam/ with a working
  ${CLAUDE_PLUGIN_ROOT} path (the old relative path never resolved from a
  marketplace-cached subdir).
- Docs: README, INSTALL, SETUP, ARCHITECTURE, CLAUDE.md, docs/PLUGINS.md,
  docs/MCP.md, docs/CLI.md, docs/HOOKS.md.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

.husky/pre-commit

@@ -36,7 +36,16 @@ else
   echo "🎨 No staged files to format."
 fi
 
-# ── 2. Run tests — commit is blocked unless all pass ────────────────────────
+# ── 2. Committed MCP build must match mcp/src ───────────────────────────────
+# mcp/build/ is committed because a plugin's MCP server starts before any
+# bootstrap could build it. Only enforced when mcp/src is part of this commit,
+# so unrelated commits are not blocked by a stale artifact.
+if git diff --cached --name-only --diff-filter=ACMR | grep -q '^mcp/src/'; then
+  echo "🔌 Checking the committed MCP build against mcp/src..."
+  node scripts/check-mcp-build.js
+fi
+
+# ── 3. Run tests — commit is blocked unless all pass ────────────────────────
 # Each suite is retried once on failure. The full run executes dozens of test
 # files concurrently, each starting its own server (plus the CLI suite's
 # spawned child processes with hard kill timeouts), so a loaded machine can