Manager abstraction + manager-dispatched lifecycle; frontends create static services

- manifest: `manager_for(runner)` — the single source of truth mapping a runner to
  its manager (systemd | caddy | path | none). deploy's `managed` now derives from it.
- lifecycle: is_active/activate/deactivate dispatch by manager instead of behavior
  (removed the stale `_is_static_frontend`, which broke once frontends became
  services). caddy → gateway reload; path → install/uninstall; none → no-op.
- cli/service: start/stop/restart and enable/disable route through the manager
  (systemctl only for systemd; static reloads the gateway; remote is a no-op);
  platform restart skips non-systemd runners.
- create: a frontend stack (react-vite/supabase) now emits a `runner: static`
  service, not a bare frontend program.

core/tests/test_caddyfile.py

@@ -10,7 +10,6 @@ from castle_core.generators.caddyfile import (
     generate_caddyfile_from_registry,
 )
 from castle_core.manifest import (
-    BuildSpec,
     ExposeSpec,
     HttpExposeSpec,
     HttpInternal,