fix: Restore all files lost during destructive rebase

A previous `git pull --rebase origin main` dropped 177 local commits,
losing 3400+ files across admin-v2, backend, studio-v2, website,
klausur-service, and many other services. The partial restore attempt
(660295e2) only recovered some files.

This commit restores all missing files from pre-rebase ref 98933f5e
while preserving post-rebase additions (night-scheduler, night-mode UI,
NightModeWidget dashboard integration).

Restored features include:
- AI Module Sidebar (FAB), OCR Labeling, OCR Compare
- GPU Dashboard, RAG Pipeline, Magic Help
- Klausur-Korrektur (8 files), Abitur-Archiv (5+ files)
- Companion, Zeugnisse-Crawler, Screen Flow
- Full backend, studio-v2, website, klausur-service
- All compliance SDKs, agent-core, voice-service
- CI/CD configs, documentation, scripts

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

studio-v2/lib/ThemeContext.tsx

@@ -0,0 +1,71 @@
+'use client'
+
+import { createContext, useContext, useState, useEffect, ReactNode } from 'react'
+
+type Theme = 'dark' | 'light'
+
+interface ThemeContextType {
+  theme: Theme
+  toggleTheme: () => void
+  isDark: boolean
+}
+
+const ThemeContext = createContext<ThemeContextType | null>(null)
+
+const STORAGE_KEY = 'bp_theme'
+
+export function ThemeProvider({ children }: { children: ReactNode }) {
+  const [theme, setTheme] = useState<Theme>('dark')
+  const [mounted, setMounted] = useState(false)
+
+  // Nach dem ersten Render: Theme aus localStorage laden
+  useEffect(() => {
+    const stored = localStorage.getItem(STORAGE_KEY) as Theme | null
+    if (stored && (stored === 'dark' || stored === 'light')) {
+      setTheme(stored)
+    }
+    setMounted(true)
+  }, [])
+
+  // Theme wechseln und speichern
+  const toggleTheme = () => {
+    const newTheme = theme === 'dark' ? 'light' : 'dark'
+    setTheme(newTheme)
+    localStorage.setItem(STORAGE_KEY, newTheme)
+  }
+
+  // Waehrend SSR: Default anzeigen
+  if (!mounted) {
+    return (
+      <ThemeContext.Provider
+        value={{
+          theme: 'dark',
+          toggleTheme: () => {},
+          isDark: true,
+        }}
+      >
+        {children}
+      </ThemeContext.Provider>
+    )
+  }
+
+  return (
+    <ThemeContext.Provider
+      value={{
+        theme,
+        toggleTheme,
+        isDark: theme === 'dark',
+      }}
+    >
+      {children}
+    </ThemeContext.Provider>
+  )
+}
+
+export function useTheme() {
+  const context = useContext(ThemeContext)
+  if (!context) {
+    throw new Error('useTheme must be used within a ThemeProvider')
+  }
+  return context
+}