Fix project/milestone association and redesign AppHeader navigation

Backend:
- routes/tasks.py: POST + PUT were silently dropping project_id,
  milestone_id, parent_id from request body — root cause of association
  not saving from the task editor
- routes/tasks.py: GET /api/tasks/:id now includes parent_title in
  response (secondary lookup when parent_id is set)
- routes/notes.py: add PATCH /api/notes/:id for partial updates (used
  by sub-task status toggle; PUT already existed but PATCH was missing)
- routes/projects.py: GET /api/projects/:id/notes now fetches milestone
  IDs and passes them via milestone_ids so tasks assigned to a milestone
  (but lacking project_id) are included in the project view
- services/notes.py: create_note() auto-sets project_id from milestone
  when milestone_id is provided and project_id is omitted; list_notes()
  gains milestone_ids param — when combined with project_id uses OR
  condition (project_id=X OR milestone_id IN (...))

Frontend:
- NoteEditorView: add MilestoneSelector; milestone resets when project
  changes; all save paths (save/create/auto-save) include milestone_id
- stores/notes.ts: add milestone_id to createNote + updateNote types
- TaskEditorView: sub-tasks now inherit milestone_id from parent task
- AppHeader: three-zone layout — brand left, Notes/Projects/Tasks/Chat
  centered (absolute positioning), right rail with status/theme/? and
  gear dropdown containing Settings/Users/Logs; mobile dropdown unchanged

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/fabledassistant/routes/notes.py

@@ -215,6 +215,25 @@ async def update_note_route(note_id: int):
     return jsonify(note.to_dict())
 
 
+@notes_bp.route("/<int:note_id>", methods=["PATCH"])
+@login_required
+async def patch_note_route(note_id: int):
+    uid = get_current_user_id()
+    data = await request.get_json()
+    fields = {}
+    for key in ("title", "body", "parent_id", "project_id", "milestone_id", "status", "priority"):
+        if key in data:
+            fields[key] = data[key]
+    if "due_date" in data:
+        fields["due_date"] = date.fromisoformat(data["due_date"]) if data["due_date"] else None
+    if "tags" in data:
+        fields["tags"] = data["tags"]
+    note = await update_note(uid, note_id, **fields)
+    if note is None:
+        return jsonify({"error": "Note not found"}), 404
+    return jsonify(note.to_dict())
+
+
 @notes_bp.route("/<int:note_id>", methods=["DELETE"])
 @login_required
 async def delete_note_route(note_id: int):