Stop tracking scheduled-emails.json runtime data store

It's mutated by the running app (scheduled job queue), not source -
committing it churns the repo with live recipient/message content.
Kept on disk, just untracked; a fresh checkout will get an empty
store created on demand by ensureStore().

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitignore

@@ -33,4 +33,7 @@ Thumbs.db
 
 # misc scratch / generated files
 temp/
-backend/public/uploads/
+backend/public/uploads/
+
+# runtime data stores (mutated by the running app, not source)
+backend/data/scheduled-emails.json

backend/data/scheduled-emails.json

@@ -1,3 +0,0 @@
-{
-  "jobs": []
-}