Refuse saving a task note in the store demo

The offline store demo has no Notes, so task:save-note is unavailable there like the other knowledge commands. CI's full build caught the missing handler.

Coven-Harness: Claude Code / claude-opus-5-5

Author: BunsDev

apps/store-desktop/src/main/demo.ts

@@ -78,6 +78,7 @@ export class StoreDemo {
       "knowledge:external": unavailable,
       "knowledge:copy": unavailable,
       "knowledge:useNotes": unavailable,
+      "task:save-note": unavailable,
       "knowledge:open": unavailable,
       "project:knowledge": unavailable,
       "project:pages": unavailable,