feat(versions): rolling-cap prune ignores pinned versions

The DELETE inside create_version now filters pin_kind IS NULL so pinned
rows (auto or manual) aren't counted toward MAX_VERSIONS=50 and aren't
candidates for deletion. Pinned versions live indefinitely regardless
of how heavy rolling autosave traffic gets on the same note.

src/fabledassistant/services/note_versions.py

@@ -47,13 +47,18 @@ async def create_version(
         await session.commit()
         await session.refresh(version)
 
-        # Prune versions beyond MAX_VERSIONS
+        # Prune rolling versions beyond MAX_VERSIONS. Pinned rows
+        # (pin_kind IS NOT NULL) are excluded from both the counted
+        # bucket and the deletion candidate set, so they survive
+        # indefinitely regardless of rolling autosave volume.
         await session.execute(
             text("""
                 DELETE FROM note_versions
                 WHERE id IN (
                     SELECT id FROM note_versions
-                    WHERE note_id = :note_id AND user_id = :user_id
+                    WHERE note_id = :note_id
+                      AND user_id = :user_id
+                      AND pin_kind IS NULL
                     ORDER BY created_at DESC
                     OFFSET :max_versions
                 )