Scope duplicate detection to same type (notes vs tasks)

create_note now only checks against existing notes (is_task=False);
create_task only checks against existing tasks (is_task=True). All three
checks (exact title, fuzzy title, semantic similarity) pass the type
filter through to list_notes and semantic_search_notes.

Adds is_task param to semantic_search_notes() so callers can restrict
results to notes or tasks independently.

Prevents a note titled "Design enemy AI" from blocking a task with the
same title, and vice versa.

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

src/fabledassistant/services/embeddings.py

@@ -80,6 +80,7 @@ async def semantic_search_notes(
     limit: int = 8,
     threshold: float = _SIMILARITY_THRESHOLD,
     project_id: int | None = None,
+    is_task: bool | None = None,
 ) -> list[tuple[float, Note]]:
     """Return up to *limit* (score, note) pairs most relevant to *query*.
 
@@ -102,6 +103,10 @@ async def semantic_search_notes(
             )
             if project_id is not None:
                 stmt = stmt.where(Note.project_id == project_id)
+            if is_task is True:
+                stmt = stmt.where(Note.status.isnot(None))
+            elif is_task is False:
+                stmt = stmt.where(Note.status.is_(None))
             if exclude_ids:
                 stmt = stmt.where(NoteEmbedding.note_id.notin_(exclude_ids))
             rows = list((await session.execute(stmt)).all())