Sprint 16: Chat-Fotos/Online/Read-Receipts, Gesundheit-Dokumente löschen, Bugfixes

- Chat: Foto-Versand (POST /api/chat/conversations/{id}/upload, media_url/media_type)
- Chat: Online-Indikator (last_seen Heartbeat, grüner Dot, 3min-Fenster)
- Chat: Read Receipts (read_at, Einzel-/Doppelhaken-Icons)
- Gesundheit: Dokument löschen (DELETE .../dokument, Datei + DB-Eintrag)
- Bug: events.user_id NOT NULL → nullable (Table-Recreation-Migration)
- Bug: scheduler INSERT user_id 0 → NULL
- Bug: Wikidata Rate-Limit: sleep 0.3s→1.0s, retries 2→4, exponentielles Backoff
- SW: by-v146, APP_VER 119

backend/database.py

@@ -453,6 +453,13 @@ def _migrate(conn_factory):
         ("users", "profil_sichtbarkeit",  "TEXT NOT NULL DEFAULT 'public'"),
         ("users", "avatar_url",           "TEXT"),
         ("places", "telefon",             "TEXT"),
+        # Chat: Foto-Versand
+        ("direct_messages", "media_url",  "TEXT"),
+        ("direct_messages", "media_type", "TEXT"),
+        # Chat: Read Receipts
+        ("direct_messages", "read_at",    "TEXT"),
+        # Chat: Online-Indikator
+        ("users", "last_seen",            "TEXT"),
     ]
     with conn_factory() as conn:
         for table, column, col_type in migrations:
@@ -648,3 +655,35 @@ def _migrate(conn_factory):
             CREATE INDEX IF NOT EXISTS idx_dog_shares_user  ON dog_shares(shared_with_id);
         """)
         logger.info("Migration: dog_shares Tabelle bereit.")
+
+        # Events: user_id NOT NULL Constraint entfernen (für Scheduler-Imports ohne User)
+        row = conn.execute(
+            "SELECT notnull FROM pragma_table_info('events') WHERE name='user_id'"
+        ).fetchone()
+        if row and row[0] == 1:
+            conn.executescript("""
+                CREATE TABLE IF NOT EXISTS events_new (
+                    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+                    user_id     INTEGER,
+                    titel       TEXT    NOT NULL,
+                    datum       TEXT    NOT NULL,
+                    uhrzeit     TEXT,
+                    lat         REAL,
+                    lon         REAL,
+                    ort_name    TEXT,
+                    typ         TEXT    NOT NULL DEFAULT 'sonstiges',
+                    beschreibung TEXT,
+                    link        TEXT,
+                    status      TEXT    NOT NULL DEFAULT 'aktiv',
+                    created_at  TEXT    NOT NULL DEFAULT (datetime('now')),
+                    quelle      TEXT    NOT NULL DEFAULT 'nutzer',
+                    external_id TEXT
+                );
+                INSERT OR IGNORE INTO events_new SELECT * FROM events;
+                DROP TABLE events;
+                ALTER TABLE events_new RENAME TO events;
+                CREATE INDEX IF NOT EXISTS idx_events_datum ON events(datum ASC);
+                CREATE UNIQUE INDEX IF NOT EXISTS idx_events_external
+                    ON events(external_id) WHERE external_id IS NOT NULL;
+            """)
+            logger.info("Migration: events.user_id NOT NULL Constraint entfernt.")