Feature: Gasthund-Zugang für Sitter

- sitting_subscriptions Tabelle (dog_id, owner_id, sitter_id, valid_until)
- POST/DELETE/GET /api/sitting-access — Zugang gewähren/widerrufen/auflisten
- GET /api/dogs gibt Gasthunde zurück (is_guest=True, sitting_until, owner_name)
- Diary POST erlaubt Sitter-Schreibzugang; PATCH/DELETE nur für Besitzer
- Dog-Switcher: GAST-Badge bei fremden Hunden
- Dog-Profil: Sitter-Zugang-Sektion (nur für Besitzer), Freund auswählen + Datum
- Diary Detail-View: Bearbeiten-Button für Gasthunde ausgeblendet

backend/routes/dogs.py

@@ -50,7 +50,30 @@ async def list_dogs(user=Depends(get_current_user)):
                WHERE ds.shared_with_id = ? AND ds.accepted_at IS NOT NULL""",
             (user["id"],)
         ).fetchall()
-    return [dict(r) for r in own] + [dict(r) for r in shared]
+        guest_rows = conn.execute("""
+            SELECT d.*, ss.id AS sub_id, ss.valid_until AS sitting_until,
+                   u.name AS owner_name, NULL AS shared_by, NULL AS share_role
+            FROM sitting_subscriptions ss
+            JOIN dogs  d ON d.id  = ss.dog_id
+            JOIN users u ON u.id  = ss.owner_id
+            WHERE ss.sitter_id = ?
+              AND ss.valid_until >= date('now')
+        """, (user["id"],)).fetchall()
+
+    result = []
+    for r in own:
+        d = dict(r)
+        d["is_guest"] = False
+        result.append(d)
+    for r in shared:
+        d = dict(r)
+        d["is_guest"] = False
+        result.append(d)
+    for r in guest_rows:
+        d = dict(r)
+        d["is_guest"] = True
+        result.append(d)
+    return result
 
 
 @router.post("")