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/static/css/components.css

@@ -1612,10 +1612,22 @@ textarea.form-control {
 }
 .rk-search-row {
   display:     flex;
+  flex-wrap:   wrap;
   gap:         var(--space-2);
   margin-bottom: var(--space-3);
   align-items: center;
 }
+.rk-search-row .rk-search {
+  min-width: 0;
+  flex-basis: 160px;
+}
+.rk-search-row .rk-view-toggle {
+  flex-shrink: 0;
+}
+@media (max-width: 480px) {
+  .rk-search-row .rk-search { flex: 1 1 100%; order: -1; }
+  .rk-search-row .rk-view-toggle { margin-left: auto; }
+}
 /* Import-Label als Button */
 .rk-imp-btn {
   cursor:      pointer;
@@ -4491,3 +4503,47 @@ textarea.form-control {
 }
 .chat-send-btn:hover   { background: var(--c-primary-dark); }
 .chat-send-btn:disabled { opacity: 0.5; cursor: default; }
+
+/* Chat: Kamera-Button */
+.chat-photo-btn {
+  width:           36px;
+  height:          36px;
+  border-radius:   50%;
+  background:      transparent;
+  color:           var(--c-text-secondary);
+  border:          none;
+  display:         flex;
+  align-items:     center;
+  justify-content: center;
+  cursor:          pointer;
+  flex-shrink:     0;
+  transition:      color var(--transition-fast);
+}
+.chat-photo-btn:hover { color: var(--c-primary); }
+
+/* Chat: Bild in Nachrichtenblase */
+.chat-bubble-img {
+  max-width:    100%;
+  max-height:   260px;
+  border-radius: var(--radius-md);
+  display:      block;
+  cursor:       pointer;
+  object-fit:   cover;
+}
+
+/* Chat: Online-Dot */
+.online-dot {
+  width:         8px;
+  height:        8px;
+  background:    #22C55E;
+  border-radius: 50%;
+  display:       inline-block;
+  flex-shrink:   0;
+}
+
+.chat-avatar-dot {
+  position: absolute;
+  bottom:   1px;
+  right:    1px;
+  border:   2px solid var(--c-surface);
+}