Make PTO creation immediately approved, add PTO deletion, and ensure cache invalidation updates individual/team/revenue capacity consistently.
Harden holiday duplicate handling (422), support PTO-day availability overrides without disabling edits, and align tests plus OpenSpec artifacts with the new behavior.
Add comprehensive E2E test for capacity calendar functionality:
- Login and navigate to capacity page
- Create test team member
- Select team member and wait for calendar
- Change availability from Full day to Half day
- Verify save completes without errors
- Verify change persists via API
Test Results:
- Backend: 76 passed ✅
- Frontend Unit: 10 passed ✅
- E2E: 132 passed, 24 skipped ✅
- New test: 2 passed (chromium + firefox) ✅
Refs: openspec/changes/headroom-foundation
