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>

docs/HOOKS.md

@@ -155,6 +155,17 @@ graph TB
 npm run install-hooks
 ```
 
+> [!IMPORTANT]
+> **Skip this entirely when the `ccam` plugin is installed.** The plugin declares
+> the same eight hooks itself (inline in `.claude-plugin/plugin.json`, each
+> running `${CLAUDE_PLUGIN_ROOT}/scripts/hook-handler.js`). Running both means
+> every event is POSTed twice — events carry no id, so ingest cannot deduplicate
+> them and every token and cost figure doubles. `scripts/plugin-bootstrap.js`
+> removes checkout-installed entries on session start (backup:
+> `~/.claude/settings.json.ccam-bak`), `install-hooks.js` warns when it detects
+> a plugin install, and `/ccam-doctor` reports any duplicates that remain. See
+> [PLUGINS.md](PLUGINS.md).
+
 > [!IMPORTANT]
 > **Hooks are a host-side step.** Claude Code runs on your host, so the hook
 > command must reference a `hook-handler.js` path that exists on the **host**.