feat: TKB shift scheduler — personnel shift planning web app

Full rewrite of METRO HMG for TKB tunnel department:
- People-based grid (18 TKB + 5 IT), year-long calendar
- Color-coded shift values (4/6/8/12/A/B/D/N/U/O)
- Drag-and-drop cells, multi-cell selection (click/ctrl/shift/drag)
- Right-click context menu with color palette
- Tunnel closure + Metro + D8 info rows (toggleable)
- Czech holidays highlighted with names
- PDF export (2-page A4 landscape, DejaVu font for Czech chars)
- Improvement proposals system
- Sticky headers (vertical + horizontal scroll)
- Cell value filter toggles in legend

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

proposals.md

@@ -0,0 +1,19 @@
+# Navrhy na vylepseni TKB Planu sluzeb
+
+---
+
+**1. 4. 2026 20:55:53** (Test User)
+
+Testovaci navrh - tlacitko pro smazani vsech bunek
+
+---
+
+**1. 4. 2026 21:00:42** (Ondra)
+
+Toto je testovaci navrh
+
+---
+
+**1. 4. 2026 22:37:55** (Ondra)
+
+Priidatt dalsi radek typu "uzavery" pro práce v metru - volitelně napojit na harmonogram metra nebo vyplňovat manuálně