feat(maestro-tui): wire --config flag + document tui in INSTALL.md (NAP-283)

- `RunConfig` grows a `config_path: Option<PathBuf>` field, plumbed from the
  umbrella binary's global `--config` flag through to `MaestroConfigFile`
  loading. Explicit `--config <path>` wins over `$MAESTRO_CONFIG` over the
  platform default; a missing file still falls back to shipped defaults.
- `docs/INSTALL.md` gains a "terminal UI" section: that `maestro tui` ships
  in the default feature set, how to opt out (`--no-default-features
  --features cli,daemon`), the `MAESTRO_DAEMON_URL` override, and a worked
  example of `[tui]` / `[tui.keymap.normal]` config pointing at the
  full action vocabulary in the design spec.
- Adds a thin-build line for `--features cli` (CLI-only client) and lists
  `tui` in the default-feature set.
- CLAUDE.md repo-layout block lists the new `maestro-tui` crate.

Closes the NAP-275 v1 epic.

CLAUDE.md

@@ -28,6 +28,7 @@ crates/
 ├── maestro-daemon/      # `maestro daemon` — tmux wrapper + WS endpoints (NAP-212, NAP-214)
 ├── maestro-registry/    # `maestro registry` — phone book + HTTP API (NAP-213, NAP-215)
 ├── maestro-web/         # standalone `maestro-web` browser UI (NAP-241, NAP-249)
+├── maestro-tui/         # `maestro tui` — ratatui session manager (NAP-275 epic)
 ├── maestro-installer/   # `maestro-install` wizard: cargo install + systemd (NAP-225)
 └── maestro-e2e/         # cross-process integration tests (NAP-217)
 web/                     # browser SPA (NAP-218)