Upgrade Tailwind CSS to version 4

Author: kernelcoffee

docs/TOFIX.md

@@ -30,15 +30,8 @@ This document tracks disabled warnings, skipped tests, and other technical debt
 
 ## Future Improvements
 
-### Higher Risk Upgrades (Deferred)
-
-| Package | Current | Latest | Notes |
-|---------|---------|--------|-------|
-| Tailwind CSS | 3.x | 4.x | Major config format changes |
-| react-router-dom | 6.x | 7.x | API changes, migration guide available |
-
 ### Code Quality
 
 - [ ] Re-enable `react-hooks/set-state-in-effect` after refactoring affected components
 - [ ] Fix APScheduler event loop conflicts to enable scheduler e2e tests in CI
-- [ ] Add more integration test coverage with mocked external services
+- [ ] Add more integration test coverage with mocked external services