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/CLI.md

@@ -61,6 +61,14 @@ ccam help
 
 If linking needed elevated permissions in your environment, setup still succeeds and prints a hint — run `npm link` once from the repo root yourself, or invoke the CLI directly with `node bin/ccam.js <command>`.
 
+### With a plugin install (no checkout)
+
+The `ccam` plugin's bootstrap writes a launcher to `~/.local/bin/ccam` on
+session start — a small script rather than a symlink into the plugin cache,
+which is replaced on every plugin update. It never overwrites a `ccam` it did
+not write, so a linked checkout keeps winning. If `~/.local/bin` is not on your
+PATH, `/ccam-doctor` says so and prints the exact `export PATH=...` line to add.
+
 ## Server Discovery
 
 The CLI finds your running dashboard the same way the Claude Code hook handler does: