Tools as PATH deployments; demote behavior from lifecycle logic

- manifest: RunPath (runner: path) — a CLI on PATH via `uv tool install`, manager
  = path, no unit/route (like remote/static).
- lifecycle/service: a path deployment's start/stop = install/uninstall (routed
  through activate/deactivate, which skip the reinstall when already on PATH).
  `castle service start/stop <tool>` and status now dispatch by manager; status
  shows the manager tag [systemd|caddy|path|none].
- config.tools() now derives from `runner: path` services, not the behavior label.
- castle-api: the "installed" flag derives from manager==path, not behavior==tool.
- create: a python-cli stack emits a `runner: path` service.

`behavior` no longer drives any runtime logic — it survives only as a display
label + `list --behavior` filter. Verified live: html2text uninstall→reinstall
round-trip via `castle service stop/start`.

core/src/castle_core/deploy.py

@@ -614,6 +614,9 @@ def _build_run_cmd(
         case "static":
             # No process — the gateway file_servers this service's root.
             return []
+        case "path":
+            # No process — installed on PATH via `uv tool install` at enable time.
+            return []
         case _:
             raise ValueError(f"Unsupported runner: {run.runner}")  # type: ignore[union-attr]