feat: Phase 2 — remove builtins layer, ServiceRegistry is installed-only

Builtins (email/calendar/files) are no longer baked into the API image.
ServiceRegistry now only knows about installed store services. When nothing
is installed, Caddy and DNS get no service routes — no hardcoded fallback.

Changes:
- service_registry.py: remove _BUILTINS_DIR, _builtin_ids, _builtin_manifest,
  _load_manifest; get() and list_all() now delegate entirely to installed services
- caddy_manager.py: remove _build_core_service_routes(); remove hardcoded
  fallback pairs from _http01_service_pairs(); empty registry → api block only
- network_manager.py: _get_service_subdomains() returns [] when no registry
- api/services/builtins/: deleted (email, calendar, files manifests)
- Tests updated throughout: removed builtin-dependent assertions, added
  installed-service fixtures, updated fallback expectations to api-only

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/service_registry.py

@@ -1,28 +1,21 @@
 """
 ServiceRegistry — single source of truth for all PIC services.
 
-Merges three layers:
+Merges two layers:
   1. Manifest defaults (config_schema.*.default)
   2. Admin-saved config from ConfigManager (cell_config.json)
-  3. Runtime state from installed store records
 
 All consumers (CaddyManager, backup, peer services endpoint) read from here
 rather than hardcoding service names or subdomains.
 """
 
-import json
 import logging
-import os
 import re
 from typing import Dict, List, Optional
 from urllib.parse import quote as _urlquote
 
 logger = logging.getLogger('picell')
 
-# Built-ins are baked into the container image at build time.
-# Do not bind-mount this path read-write in docker-compose.
-_BUILTINS_DIR = os.path.join(os.path.dirname(__file__), 'services', 'builtins')
-
 _SUBDOMAIN_RE = re.compile(r'^[a-z][a-z0-9-]{0,30}$')
 _BACKEND_RE   = re.compile(r'^[A-Za-z0-9._-]+:\d{1,5}$')
 _RESERVED_SUBS = frozenset({'api', 'webui', 'admin', 'www', 'ns1', 'ns2', 'git', 'registry', 'install'})
@@ -33,29 +26,6 @@ class ServiceRegistry:
     def __init__(self, config_manager):
         self._cm = config_manager
 
-    # ── Manifest loading ──────────────────────────────────────────────────
-
-    def _load_manifest(self, path: str) -> Optional[Dict]:
-        try:
-            with open(path) as f:
-                return json.load(f)
-        except Exception as e:
-            logger.warning('ServiceRegistry: failed to load manifest %s: %s', path, e)
-            return None
-
-    def _builtin_ids(self) -> List[str]:
-        if not os.path.isdir(_BUILTINS_DIR):
-            return []
-        return sorted(
-            d for d in os.listdir(_BUILTINS_DIR)
-            if os.path.isfile(os.path.join(_BUILTINS_DIR, d, 'manifest.json'))
-        )
-
-    def _builtin_manifest(self, service_id: str) -> Optional[Dict]:
-        return self._load_manifest(
-            os.path.join(_BUILTINS_DIR, service_id, 'manifest.json')
-        )
-
     # ── Config merging ────────────────────────────────────────────────────
 
     _TYPE_COERCIONS = {'integer': int, 'string': str, 'boolean': bool}
@@ -83,22 +53,16 @@ class ServiceRegistry:
 
     def get(self, service_id: str) -> Optional[Dict]:
         """Return manifest + merged config for one service, or None if unknown."""
-        manifest = self._builtin_manifest(service_id)
-        if manifest is None:
-            record = self._cm.get_installed_services().get(service_id)
-            if record:
-                manifest = record.get('manifest')
+        record = self._cm.get_installed_services().get(service_id)
+        if not record:
+            return None
+        manifest = record.get('manifest')
         if not manifest:
             return None
         return {**manifest, 'config': self._merged_config(manifest)}
 
     def list_active(self) -> List[Dict]:
-        """Return only installed store services, each with merged config.
-
-        Unlike list_all(), builtins are excluded. Use this wherever the
-        intent is "what has the admin chosen to run?" rather than "everything
-        the registry knows about."
-        """
+        """Return all installed store services, each with merged config."""
         results = []
         for _svc_id, record in self._cm.get_installed_services().items():
             manifest = record.get('manifest') or {}
@@ -107,27 +71,8 @@ class ServiceRegistry:
         return results
 
     def list_all(self) -> List[Dict]:
-        """
-        Return all services — builtins first, then installed store services —
-        each with merged config attached as the 'config' key.
-        """
-        results: List[Dict] = []
-        seen: set = set()
-
-        for svc_id in self._builtin_ids():
-            manifest = self._builtin_manifest(svc_id)
-            if manifest:
-                results.append({**manifest, 'config': self._merged_config(manifest)})
-                seen.add(svc_id)
-
-        for svc_id, record in self._cm.get_installed_services().items():
-            if svc_id in seen:
-                continue
-            manifest = record.get('manifest') or {}
-            if manifest.get('id'):
-                results.append({**manifest, 'config': self._merged_config(manifest)})
-
-        return results
+        """Return all installed store services, each with merged config attached as the 'config' key."""
+        return self.list_active()
 
     def get_caddy_routes(self) -> List[Dict]:
         """