feat(workspace): turn a branch into its own note, merge notes

- Extract: button on the bullet (desktop) or /extract (/notiz). The bullet
  becomes the title (hashtags stay at the link), its children the content
  of a new note in the same folder with the source's shares (a foreign
  source owner gets write access); the branch becomes [[title]] through
  the operation log, so open editors follow.
- Merge: drop a note onto another in the sidebar or use "Mit anderer
  Notiz zusammenführen…" in the note header. The own source is appended
  as an h2 section with its bullets below and goes to the trash; the toast
  offers a complete undo.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/features/workspace/DocumentEditor.tsx

@@ -17,6 +17,7 @@ import {
   Check,
   CloudOff,
   AlertTriangle,
+  GitMerge,
 } from 'lucide-react';
 import { Document, DocumentBlock, User } from '../../lib/types';
 import { api } from '../../lib/api';
@@ -44,6 +45,8 @@ export interface DocumentEditorProps {
   onBackMobile?: () => void;
   onOpenTask?: (taskId: string) => void;
   onSaveStatusChange?: (status: DocSaveStatus, errorMsg?: string) => void;
+  /** Opens the dialog to merge this note into another one (own notes only) */
+  onRequestMerge?: (doc: Document) => void;
 }
 
 import { EmojiPickerModal } from './EmojiPickerModal';
@@ -190,6 +193,7 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
   onBackMobile,
   onOpenTask,
   onSaveStatusChange,
+  onRequestMerge,
 }) => {
   const [doc, setDoc] = useState<Document | null>(initialDoc || null);
   const [title, setTitle] = useState<string>(initialDoc?.title || '');
@@ -375,14 +379,39 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
       .catch(() => {});
   }, [otherPeople.length]);
 
-  // Short hint at the bottom of the editor (blocked actions, skipped undo)
+  // Short hint at the bottom of the editor (blocked actions, skipped undo), optionally with one action
   const [notice, setNotice] = useState<string | null>(null);
+  const [noticeAction, setNoticeAction] = useState<{ label: string; run: () => void } | null>(null);
   const noticeTimerRef = useRef<number | null>(null);
-  const showNotice = useCallback((message: string) => {
+  const showNotice = useCallback((message: string, action?: { label: string; run: () => void }) => {
     setNotice(message);
+    setNoticeAction(action || null);
     if (noticeTimerRef.current !== null) window.clearTimeout(noticeTimerRef.current);
-    noticeTimerRef.current = window.setTimeout(() => setNotice(null), 3500);
+    noticeTimerRef.current = window.setTimeout(() => {
+      setNotice(null);
+      setNoticeAction(null);
+    }, action ? 7000 : 3500);
   }, []);
+
+  // A bullet with its children becomes a note of its own; the server swaps the branch for a [[link]]
+  // and this editor receives that change through the normal sync
+  const handleExtractBlock = useCallback(
+    async (blockId: string) => {
+      const engine = engineRef.current;
+      try {
+        await engine?.syncNow(); // the branch as typed so far
+        const created = await api.extractBranch(docId, blockId, engine?.clientId || '');
+        await engine?.syncNow();
+        showNotice(`In eigene Notiz „${created.title}“ umgewandelt`, {
+          label: 'Öffnen',
+          run: () => onOpenDocBlock?.(created.id),
+        });
+      } catch (err: any) {
+        showNotice(err?.message || 'Umwandeln fehlgeschlagen');
+      }
+    },
+    [docId, onOpenDocBlock, showNotice]
+  );
   useEffect(() => () => {
     if (noticeTimerRef.current !== null) window.clearTimeout(noticeTimerRef.current);
   }, []);
@@ -817,6 +846,16 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
                 >
                   <Users className="w-3.5 h-3.5" />
                 </button>
+                {onRequestMerge && doc.isOwner && !inTrash && (
+                  <button
+                    type="button"
+                    onClick={() => onRequestMerge(doc)}
+                    className="btn-icon"
+                    title="Mit anderer Notiz zusammenführen…"
+                  >
+                    <GitMerge className="w-3.5 h-3.5" />
+                  </button>
+                )}
               </div>
             );
           })()}
@@ -969,6 +1008,7 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
                 canEdit={canEdit}
                 levelOffset={levelOffset}
                 onZoomBlock={setZoomedBlockId}
+                onExtractBlock={canEdit ? handleExtractBlock : undefined}
                 onUpdateBlock={handleUpdateBlock}
                 onUpdateBlocks={handleUpdateBlocks}
                 onCreateBlock={handleCreateBlock}
@@ -1056,6 +1096,7 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
               canEdit={canEdit}
               levelOffset={0}
               onZoomBlock={setZoomedBlockId}
+              onExtractBlock={canEdit ? handleExtractBlock : undefined}
               onUpdateBlock={handleUpdateBlock}
               onUpdateBlocks={handleUpdateBlocks}
               onCreateBlock={handleCreateBlock}
@@ -1084,7 +1125,20 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
           role="status"
           className="fixed bottom-6 left-1/2 -translate-x-1/2 z-50 max-w-[90vw] px-3 py-2 rounded-card text-xs text-main bg-panel-elevated border border-border shadow-panel"
         >
-          {notice}
+          <span>{notice}</span>
+          {noticeAction && (
+            <button
+              type="button"
+              onClick={() => {
+                noticeAction.run();
+                setNotice(null);
+                setNoticeAction(null);
+              }}
+              className="ml-3 font-semibold text-accent hover:underline min-h-[44px] sm:min-h-0"
+            >
+              {noticeAction.label}
+            </button>
+          )}
         </div>
       )}
     </div>