feat(M5): Plugin-MiniApps — dms, mail, wiki, graph_rag, automation (#363)

- 5 Manifest-Beiträge (MiniAppContribution): dms_folders (dms:read), mail_unread (mail:read), wiki_recent (wiki:read), graph_overview (graph:read), automation_status (automation:read) — je settings_schema max_items, order 60-100
- 5 Frontend-Widgets auf bestehenden API-Clients (keine neuen Backend-Endpoints): DmsFoldersWidget, MailUnreadWidget, WikiRecentWidget, GraphOverviewWidget, AutomationStatusWidget
- MiniAppHost-Registry +5; tsc clean, build OK
- Tests: M5 7/7 (TDD rot->gruen), Backend-Regression 53/53, Vitest 22/22

app/plugins/builtins/mail/plugin.py

@@ -12,6 +12,7 @@ from app.plugins.manifest import (
     FrontendMenuItem,
     FrontendPageRoute,
     FrontendSettingsPage,
+    MiniAppContribution,
     PluginManifest,
     PluginRouteDef,
 )
@@ -138,6 +139,25 @@ class MailPlugin(BasePlugin):
         ],
         events=[],
         migrations=["0001_initial.sql", "0006_flag_type.sql", "0007_sync_queue.sql", "0008_sync_queue_deleted_at.sql", "0009_remove_mail_soft_delete.sql", "0010_add_deleted_at.sql"],
+        miniapps=[
+            MiniAppContribution(
+                app_id="mail_unread",
+                name="Postfach-Status",
+                icon="Mail",
+                description="Ungelesene E-Mails je Konto und Ordner.",
+                permission="mail:read",
+                settings_schema={
+                    "fields": [
+                        {"name": "max_items", "label": "Max. Ordner", "type": "number", "default": 6},
+                    ]
+                },
+                col_span=2,
+                row_span=1,
+                hosts=["chat", "dashboard", "window"],
+                component="@/components/dashboard/MailUnreadWidget",
+                order=70,
+            ),
+        ],
         permissions=["mail:read", "mail:send", "mail:config", "mail:share", "mail:write", "mail:delete"],
         menu_items=[
             FrontendMenuItem(label_key='nav.mail', label='E-Mail', path='/mail', icon='Mail', order=30, permission='mail:read'),