fix: post-Phase-0 corrections — data-dir bind mounts, reserved subdomains, list_active()

Three related fixes discovered during review of Phase 0 and Phase 1 manifests:

1. validate_rendered_compose(): add allowed_data_dir param. After ${PIC_DATA_DIR}
   substitution, compose templates produce absolute paths; without this the
   validator would reject every service install.  ServiceComposer.write_compose()
   now passes its resolved data_dir so only the designated data directory is
   exempt — /etc, /proc, docker.sock etc. still blocked.

2. _RESERVED_SUBDOMAINS: remove service-level subdomains (mail, calendar, files,
   webdav, webmail). The reserved list should protect PIC infrastructure endpoints
   (api, webui, admin) — not service subdomains that official store services
   (calendar, files, webmail) must be allowed to claim.  Aligns with the
   existing _RESERVED_SUBS in service_registry.py.

3. ServiceRegistry.list_active(): new method returning only installed store
   services (no builtins). This is the forward-looking API that Phase 2 will
   make the primary read path once builtins are deleted. Adding it now unblocks
   the QA agent's test_optional_services_feature.py which was already testing
   the expected Phase 2 behaviour.

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

tests/test_manifest_validator.py

@@ -164,13 +164,15 @@ class TestValidateManifest(unittest.TestCase):
         ok, errs = validate_manifest(m)
         self.assertTrue(ok)
 
-    def test_subdomain_calendar_rejected(self):
+    def test_subdomain_calendar_passes(self):
+        # calendar/files/webmail/etc are service subdomains, not infrastructure;
+        # official PIC store services need to claim them.
         ok, errs = validate_manifest(_minimal_manifest(subdomain='calendar'))
-        self.assertFalse(ok)
+        self.assertTrue(ok, errs)
 
-    def test_subdomain_files_rejected(self):
+    def test_subdomain_files_passes(self):
         ok, errs = validate_manifest(_minimal_manifest(subdomain='files'))
-        self.assertFalse(ok)
+        self.assertTrue(ok, errs)
 
     # ── extra_subdomains ─────────────────────────────────────────────────
 
@@ -489,6 +491,56 @@ class TestValidateRenderedCompose(unittest.TestCase):
         ok, errs = validate_rendered_compose(yaml_text)
         self.assertTrue(ok)
 
+    def test_absolute_volume_under_allowed_data_dir_passes(self):
+        # After ${PIC_DATA_DIR} substitution, compose templates produce absolute
+        # paths like /data/services/email/mail:/var/mail. These must be allowed
+        # when allowed_data_dir is set to the same prefix.
+        yaml_text = (
+            'services:\n'
+            '  mail:\n'
+            '    image: svc-email:latest\n'
+            '    command: ["postfix"]\n'
+            '    volumes:\n'
+            '      - /data/services/email/mail:/var/mail\n'
+            '      - /data/services/email/config:/tmp/config\n'
+            'networks:\n'
+            '  cell-network:\n'
+            '    external: true\n'
+        )
+        ok, errs = validate_rendered_compose(yaml_text, allowed_data_dir='/data')
+        self.assertTrue(ok, errs)
+
+    def test_absolute_volume_outside_allowed_data_dir_still_rejected(self):
+        yaml_text = (
+            'services:\n'
+            '  app:\n'
+            '    image: nginx\n'
+            '    volumes:\n'
+            '      - /etc/passwd:/etc/passwd\n'
+            'networks:\n'
+            '  cell-network:\n'
+            '    external: true\n'
+        )
+        ok, errs = validate_rendered_compose(yaml_text, allowed_data_dir='/data')
+        self.assertFalse(ok)
+        self.assertTrue(any('bind mount' in e for e in errs))
+
+    def test_absolute_volume_rejected_when_no_allowed_data_dir(self):
+        yaml_text = (
+            'services:\n'
+            '  app:\n'
+            '    image: nginx\n'
+            '    volumes:\n'
+            '      - /data/services/email/mail:/var/mail\n'
+            'networks:\n'
+            '  cell-network:\n'
+            '    external: true\n'
+        )
+        # Without allowed_data_dir, even /data paths are rejected
+        ok, errs = validate_rendered_compose(yaml_text)
+        self.assertFalse(ok)
+        self.assertTrue(any('bind mount' in e for e in errs))
+
     # ── cap_add ──────────────────────────────────────────────────────────
 
     def test_compose_cap_add_sys_admin_rejected(self):