Improve project/task/sub-task workflows across backend and web

Backend:
- notes.py: add parent_id filter to list_notes()
- routes/notes.py: expose project_id, milestone_id, parent_id, type
  query params on GET /api/notes
- milestones.py: add find_milestone_by_title() (cross-project search)
- tools.py: list_notes project filter + updated_at; list_tasks milestone
  without project; tag_mode default add; fail-fast project resolution

Web frontend:
- TaskEditorView: add sub-tasks section (fetch, toggle, create inline);
  pre-fill projectId/milestoneId/parentId from URL query params on new task
- ProjectView: add + button in Todo kanban column header linking to
  /tasks/new?projectId=X&milestoneId=Y for quick task creation

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

src/fabledassistant/services/milestones.py

@@ -53,6 +53,18 @@ async def get_milestone_by_title(user_id: int, project_id: int, title: str) -> M
         return result.scalars().first()
 
 
+async def find_milestone_by_title(user_id: int, title: str) -> Milestone | None:
+    """Find a milestone by title across ALL projects for this user (case-insensitive)."""
+    async with async_session() as session:
+        result = await session.execute(
+            select(Milestone).where(
+                Milestone.user_id == user_id,
+                func.lower(Milestone.title) == func.lower(title.strip()),
+            ).order_by(Milestone.id).limit(1)
+        )
+        return result.scalars().first()
+
+
 async def get_or_create_milestone(user_id: int, project_id: int, title: str) -> Milestone:
     milestone = await get_milestone_by_title(user_id, project_id, title)
     if milestone: