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/OutlinerBlock.tsx

@@ -23,6 +23,7 @@ import {
   Image as ImageIcon,
   Mic,
   AudioLines,
+  FileOutput,
 } from 'lucide-react';
 import { DocumentBlock, BlockType } from '../../lib/types';
 import { LinkModal } from './LinkModal';
@@ -41,7 +42,7 @@ import { api } from '../../lib/api';
 import { safeHref } from '../../lib/safeUrl';
 
 export interface SlashCommand {
-  type: BlockType | 'link' | 'dictation';
+  type: BlockType | 'link' | 'dictation' | 'extract';
   label: string;
   desc: string;
   icon: React.ReactNode;
@@ -60,6 +61,7 @@ const SLASH_COMMANDS: SlashCommand[] = [
   { type: 'code', label: '/code', desc: 'Code-Block mit Syntax', icon: <Code className="w-3.5 h-3.5" /> },
   { type: 'callout', label: '/callout', desc: 'Hinweisbox', icon: <MessageSquare className="w-3.5 h-3.5" /> },
   { type: 'divider', label: '/divider', desc: 'Trennlinie', icon: <Minus className="w-3.5 h-3.5" /> },
+  { type: 'extract', label: '/extract', desc: 'Ast als eigene Notiz', icon: <FileOutput className="w-3.5 h-3.5" />, aliases: ['notiz', 'auslagern'] },
   { type: 'image', label: '/image', desc: 'Bilder hochladen oder verlinken', icon: <ImageIcon className="w-3.5 h-3.5" />, media: true, aliases: ['bild', 'foto'] },
   { type: 'audio', label: '/audio', desc: 'Sprachnotiz oder Audiodatei', icon: <Mic className="w-3.5 h-3.5" />, media: true, aliases: ['sprachnotiz'] },
   { type: 'dictation', label: '/diktat', desc: 'Sprechen statt tippen', icon: <AudioLines className="w-3.5 h-3.5" />, media: true, aliases: ['dictate'] },
@@ -76,6 +78,8 @@ export interface OutlinerBlockProps {
   canEdit: boolean;
   levelOffset?: number;
   onZoomBlock?: (blockId: string) => void;
+  /** Turns this bullet and its children into a note of its own */
+  onExtractBlock?: (blockId: string) => void;
   onUpdateBlock: (updated: DocumentBlock, immediate?: boolean) => void;
   onCreateBlockBelow: (afterBlockId: string, newContent?: string) => void;
   onDeleteBlock: (blockId: string, deleteSubtree?: boolean) => void;
@@ -123,6 +127,7 @@ export const OutlinerBlock: React.FC<OutlinerBlockProps> = ({
   canEdit,
   levelOffset = 0,
   onZoomBlock,
+  onExtractBlock,
   onUpdateBlock,
   onCreateBlockBelow,
   onDeleteBlock,
@@ -362,11 +367,13 @@ export const OutlinerBlock: React.FC<OutlinerBlockProps> = ({
       (c) =>
         (!c.media || emptyBullet) &&
         (c.type !== 'dictation' || ['server', 'browser'].includes(currentVoiceConfig().mode)) &&
+        // The bullet's text becomes the title of the new note
+        (c.type !== 'extract' || (!emptyBullet && !!onExtractBlock)) &&
         (c.label.toLowerCase().includes(cmdQuery) ||
           c.desc.toLowerCase().includes(cmdQuery) ||
           (c.aliases || []).some((a) => a.includes(cmdQuery)))
     );
-  }, [slashSearch, localContent]);
+  }, [slashSearch, localContent, onExtractBlock]);
 
   const applySlashCommand = (cmd: SlashCommand) => {
     setSlashSearch(null);
@@ -377,6 +384,13 @@ export const OutlinerBlock: React.FC<OutlinerBlockProps> = ({
       setShowLinkModal(true);
       return;
     }
+    if (cmd.type === 'extract') {
+      setLocalContent(clean);
+      localContentRef.current = clean;
+      flushDebounce(clean);
+      onExtractBlock?.(block.id);
+      return;
+    }
     if (cmd.media) {
       // The typed "/image" must not stay in the synced text; the block type changes only after the upload
       setLocalContent('');
@@ -1272,6 +1286,18 @@ export const OutlinerBlock: React.FC<OutlinerBlockProps> = ({
         )}
       </div>
 
+      {/* Branch into its own note (desktop; phones use /extract) */}
+      {canEdit && onExtractBlock && localContent.trim() !== '' && !mediaPicker && (
+        <button
+          type="button"
+          onClick={() => onExtractBlock(block.id)}
+          className="hidden sm:block opacity-0 group-hover:opacity-100 focus:opacity-100 p-0.5 text-faint hover:text-accent rounded-btn transition-opacity shrink-0"
+          title="In eigene Notiz umwandeln (mit allen Unterpunkten)"
+        >
+          <FileOutput className="w-3.5 h-3.5" />
+        </button>
+      )}
+
       {/* Zoom / Focus button on hover */}
       <button
         type="button"