feat: light/dark theme toggle (WIP)

CSS-override approach: light-mode rules in index.css target Tailwind utility
classes when body.light is present — no component rewrites. Theme persists
in localStorage. Toggle button next to FPD in toolbar.

Custom classes for elements that needed mode-specific styling:
- pms-cell (Práce mimo směnu cells)
- pms-label (rotated PMS column header)
- pms-week (week-row PMS cell, merges visually in light mode)
- schedule-wrapper (decouples table container from weekend cell tint)

Also: vite.config.ts proxy 3080 → 3090 to point at the TKB server.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web/vite.config.ts

@@ -6,7 +6,7 @@ export default defineConfig({
   plugins: [react(), tailwindcss()],
   server: {
     proxy: {
-      '/api': 'http://localhost:3080',
+      '/api': 'http://localhost:3090',
     },
   },
 })