Initial commit: TKB Timeshift Schedule Management Application

- Next.js 15.2.4 with React 19 and TypeScript
- Monthly schedule generator with Excel-like formatting
- Complete employee list from example.xlsx (18 employees)
- Excel-style column naming (A, B, C, ..., Z, AA, AB, ...)
- Counter-clockwise text rotation for data values
- Weekend highlighting and shift color coding
- Team selection for TKB, METRO, D8
- 7 days from previous month + full current month date range
- jspreadsheet integration for Excel-like interface

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

hooks/use-mobile.ts

@@ -0,0 +1,19 @@
+import * as React from "react"
+
+const MOBILE_BREAKPOINT = 768
+
+export function useIsMobile() {
+  const [isMobile, setIsMobile] = React.useState<boolean | undefined>(undefined)
+
+  React.useEffect(() => {
+    const mql = window.matchMedia(`(max-width: ${MOBILE_BREAKPOINT - 1}px)`)
+    const onChange = () => {
+      setIsMobile(window.innerWidth < MOBILE_BREAKPOINT)
+    }
+    mql.addEventListener("change", onChange)
+    setIsMobile(window.innerWidth < MOBILE_BREAKPOINT)
+    return () => mql.removeEventListener("change", onChange)
+  }, [])
+
+  return !!isMobile
+}