Phase 3 Step 6: Complete Scheduler Integration with Bug Fixes

Implemented complete scheduler integration with automatic schedule loading,
orphaned scan cleanup, and conversion to local timezone for better UX.

Backend Changes:
- Added load_schedules_on_startup() to load enabled schedules on app start
- Implemented cleanup_orphaned_scans() to handle crashed/interrupted scans
- Converted scheduler from UTC to local system timezone throughout
- Enhanced scheduler service with robust error handling and logging

Frontend Changes:
- Updated all schedule UI templates to display local time instead of UTC
- Improved timezone indicators and user messaging
- Removed confusing timezone converter (no longer needed)
- Updated quick templates and help text for local time

Bug Fixes:
- Fixed critical timezone bug causing cron expressions to run at wrong times
- Fixed orphaned scans stuck in 'running' status after system crashes
- Improved time display clarity across all schedule pages

All schedules now use local system time for intuitive scheduling.

docs/ai/PHASE3.md

@@ -1368,7 +1368,7 @@ async function loadScanTrend() {
 
 ---
 
-### Step 6: Scheduler Integration ✅ (Day 10)
+### Step 6: Scheduler Integration ✅ COMPLETE (Day 10)
 **Priority: CRITICAL** - Complete scheduled execution
 
 **Tasks:**