fix: remove stale backup file agent_scheduler.py.bak (fixes #1964)

Remove dead code - stale backup file that was tracked in git but
unreferenced. Also add *.bak to .gitignore to prevent recurrence.

Co-authored-by: MervinPraison <MervinPraison@users.noreply.github.com>

Author: praisonai-triage-agent[bot]

.gitignore

@@ -88,6 +88,9 @@ issue_details.json
 .internal
 .praisonai
 
+# Backup files
+*.bak
+
 # Rust / Cargo
 target/
 Cargo.lock