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/lifecycle.py

@@ -198,6 +198,8 @@ async def activate(name: str, config: CastleConfig, root: Path) -> ActionResult:
         prog, comp = _program_for(name, config)
         if comp is None:
             return ActionResult(name, "activate", "error", f"unknown program '{prog}'")
+        if _on_path(prog):  # already installed — skip the (slow) editable reinstall
+            return ActionResult(name, "activate", "ok", f"{name}: on PATH")
         return await run_action("install", prog, comp, root)
 
     if manager == "none":