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>

backend/frontend/studio.py

@@ -0,0 +1,39 @@
+"""
+BreakPilot Studio Frontend
+
+Dieses Modul serviert das Studio-Frontend aus der modularen Architektur.
+
+Refactored: 2024-12-18
+- Modulare Architektur aus frontend/modules/
+- Dashboard mit Kachel-Navigation als Startansicht
+- Module: Dashboard, Worksheets, Correction, Jitsi, Letters, Messenger
+"""
+
+from fastapi import APIRouter
+from fastapi.responses import HTMLResponse
+
+# Import der modularen Architektur
+from .studio_modular import get_studio_html
+
+router = APIRouter()
+
+
+@router.get("/app", response_class=HTMLResponse)
+@router.get("/studio", response_class=HTMLResponse)
+def app_ui():
+    """
+    Rendert das BreakPilot Studio Frontend.
+
+    Das HTML wird dynamisch aus den Modulen generiert:
+    - BaseLayoutModule: TopBar, Sidebar, Theme Toggle
+    - DashboardModule: Start-Ansicht mit Kacheln
+    - WorksheetsModule: Arbeitsblaetter Studio
+    - CorrectionModule: Klausurkorrektur
+    - JitsiModule: Videokonferenzen
+    - LettersModule: Elternbriefe
+    - MessengerModule: Matrix Messenger
+    - SchoolModule: Schulverwaltung
+    - ContentCreatorModule: Content Creator (H5P Integration)
+    - ContentFeedModule: Content Discovery & Rating
+    """
+    return get_studio_html()