fix(plugins): set is_core=True for all built-in plugins

All built-in plugins should be auto-activated. The is_core flag was
only set on some plugins, leaving Mail, DMS, Calendar, Automation,
Unified Search etc. inactive by default.

app/plugins/builtins/ai_proactive/plugin.py

@@ -42,7 +42,7 @@ class AIProactivePlugin(BasePlugin):
             "ai_proactive:write",
             "ai_proactive:config",
         ],
-        is_core=False,
+        is_core=True,
         settings_pages=[
             FrontendSettingsPage(path='ai-proactive', label_key='settings.aiProactive', label='Proactive AI', component='@/pages/ProactiveAISettings', icon='Sparkles', order=61),
         ],

app/plugins/builtins/automation/plugin.py

@@ -69,7 +69,7 @@ class AutomationPlugin(BasePlugin):
             "agents:delete",
             "agents:execute",
         ],
-        is_core=False,
+        is_core=True,
         menu_items=[
             FrontendMenuItem(
                 label_key="nav.workflows",

app/plugins/builtins/forgejo_error_reporter/plugin.py

@@ -23,7 +23,7 @@ class ForgejoErrorReporterPlugin(BasePlugin):
         version="1.0.0",
         display_name="Forgejo Error Reporter",
         description="Automatically reports errors to Forgejo as issues. Test environment only.",
-        is_core=False,
+        is_core=True,
         dependencies=[],
         events=[],
         migrations=[],

app/plugins/builtins/system_notif/plugin.py

@@ -43,7 +43,7 @@ class SystemNotifPlugin(BasePlugin):
         ],
         migrations=[],
         permissions=["system_notif:read"],
-        is_core=False,
+        is_core=True,
         settings_pages=[
             FrontendSettingsPage(path='notifications', label_key='settings.notifications', label='Notifications', component='@/pages/SettingsNotifications', icon='Bell', order=40),
         ],

app/plugins/builtins/unified_search/plugin.py

@@ -39,7 +39,7 @@ class UnifiedSearchPlugin(BasePlugin):
         ],
         migrations=["0001_initial.sql", "0002_embeddings.sql", "0003_add_deleted_at.sql"],
         permissions=["search:read", "search:admin"],
-        is_core=False,
+        is_core=True,
         page_routes=[
             FrontendPageRoute(path='/search', component='@/pages/GlobalSearchResults', protected=True),
         ],