feat: raw-TCP exposure with castle-managed TLS + reach model

Expose raw-TCP services (postgres) by name at <name>.<domain>:<port> and
cut the gateway's ACME wildcard cert onto them so they present a trusted
cert. Replaces the proxy/public booleans with a single `reach` enum
(off|internal|public); legacy input still parses via derived accessors.

Core:
- expose.tcp{port,tls} + TlsSpec(material: pair|combined|off, reload)
- tls.py: materialize cert files from Caddy's wildcard, reconcile on
  renewal; `castle tls` CLI; optional cert_obtained events-exec hook
  (gateway.cert_hook, gated so a plugin-less Caddy still parses)
- apply waits (bounded) for the wildcard to issue before materializing so
  a fresh-node TLS service starts with its cert in place, then scopes
  materialization to the deployments being applied
- reach: internal|public requires an expose block (no silent no-op);
  public raw-TCP guarded until tunnel support lands
- chain.pem (${tls_ca}) is the issuer chain (leaf stripped), a real CA
  bundle distinct from cert.pem
- one shared ${...} resolver (resolve_placeholders) for env and container
  run fields; run.env now expands like volumes/args; $$ escapes a literal
- validate the generated Caddyfile before reloading the gateway so an
  invalid config never degrades routing

Docs: docs/tcp-exposure.md. Tests cover reach/expose validation,
placeholder expansion + escape, issuer-chain material, TLS materialize.

castle-api/src/castle_api/routes.py

@@ -114,7 +114,7 @@ def _summary_from_service(
     if svc.expose and svc.expose.http:
         port = svc.expose.http.internal.port
         health_path = svc.expose.http.health_path
-    subdomain = name if svc.proxy else None
+    subdomain = name if svc.http_exposed else None
 
     managed = bool(svc.manage and svc.manage.systemd and svc.manage.systemd.enable)
 
@@ -288,7 +288,7 @@ def _service_from_spec(name: str, svc: SystemdDeployment, config: object) -> Ser
         port = svc.expose.http.internal.port
         health_path = svc.expose.http.health_path
     # Exposed at <name>.<domain> when the proxy checkbox is on.
-    subdomain = name if svc.proxy else None
+    subdomain = name if svc.http_exposed else None
 
     managed = bool(svc.manage and svc.manage.systemd and svc.manage.systemd.enable)
     systemd_info = _make_systemd_info(name) if managed else None