fix(annotations): note LWW re-save 500'd — UserID missing from the sync update params

Pin-first batch for H3: freeze web annotation CRUD response shapes
(create 201 / update 200 / delete 204; full sqlc row models) before
the stack consolidation touches anything.

The new pins immediately caught a live server bug the 28 unit tests
could never see (annotations_test.go is pure-unit: keys and compare
logic, no DB): applyNoteLWW built UpdateMediaNoteForSyncParams without
UserID, so the query's WHERE id=$1 AND user_id=$13 compared against
zero — every dedup-hit note re-save (same content+position) returned
500 "update note: no rows in result set" and the update never landed.
The bookmark twin passes UserID and works; the note stack is the clone
that dropped the field.

Fix: pass UserID in the params (one line). Pins go green and become
the regression net; changelog records the new surfaces.

internal/sync/annotations.go

@@ -613,6 +613,7 @@ func (s *AnnotationService) applyNoteLWW(ctx context.Context, req SaveNoteReques
 
 	note, err := s.db.UpdateMediaNoteForSync(ctx, database.UpdateMediaNoteForSyncParams{
 		ID:                 existing.ID,
+		UserID:             req.UserID,
 		Content:            req.Content,
 		Position:           pgText(req.Position),
 		PercentageLocation: pgFloat8(req.PercentageLocation),