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/tests/conftest.py

@@ -42,6 +42,10 @@ def castle_root(tmp_path: Path) -> Generator[Path, None, None]:
             },
         },
         "services": {
+            "test-tool": {
+                "program": "test-tool",
+                "run": {"runner": "path"},
+            },
             "test-svc": {
                 "program": "test-svc-comp",
                 "description": "Test service",