fix(workspace-server): distinguish DB error from not-found in PatchAbilities

The existence-check condition `err != nil || !exists` conflated two
semantically different outcomes into a single 404 response:

  - err != nil    → DB/internal error → should be 500
  - !exists       → workspace absent  → 404 is correct

Fix: split into two explicit branches. DB errors now return 500 with
a logged reason. The not-found case remains 404.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

workspace-server/internal/handlers/workspace_abilities.go

@@ -51,7 +51,12 @@ func PatchAbilities(c *gin.Context) {
 	var exists bool
 	if err := db.DB.QueryRowContext(ctx,
 		`SELECT EXISTS(SELECT 1 FROM workspaces WHERE id = $1 AND status != 'removed')`, id,
-	).Scan(&exists); err != nil || !exists {
+	).Scan(&exists); err != nil {
+		log.Printf("PatchAbilities: workspace existence check for %s: %v", id, err)
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "internal error"})
+		return
+	}
+	if !exists {
 		c.JSON(http.StatusNotFound, gin.H{"error": "workspace not found"})
 		return
 	}