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/learning_units_api.py

@@ -0,0 +1,197 @@
+from typing import List, Dict, Any, Optional
+from datetime import datetime
+
+from fastapi import APIRouter, HTTPException
+from pydantic import BaseModel
+
+from learning_units import (
+    LearningUnit,
+    LearningUnitCreate,
+    LearningUnitUpdate,
+    list_learning_units,
+    get_learning_unit,
+    create_learning_unit,
+    update_learning_unit,
+    delete_learning_unit,
+)
+
+
+router = APIRouter(
+    prefix="/learning-units",
+    tags=["learning-units"],
+)
+
+
+# ---------- Payload-Modelle für das Frontend ----------
+
+
+class LearningUnitCreatePayload(BaseModel):
+    """
+    Payload so, wie er aus dem Frontend kommt:
+    {
+      "student": "...",
+      "subject": "...",
+      "title": "...",
+      "grade": "7a"
+    }
+    """
+    student: Optional[str] = None
+    subject: Optional[str] = None
+    title: Optional[str] = None
+    grade: Optional[str] = None
+
+
+class AttachWorksheetsPayload(BaseModel):
+    worksheet_files: List[str]
+
+
+class RemoveWorksheetPayload(BaseModel):
+    worksheet_file: str
+
+
+# ---------- Hilfsfunktion: Backend-Modell -> Frontend-Objekt ----------
+
+
+def unit_to_frontend_dict(lu: LearningUnit) -> Dict[str, Any]:
+    """
+    Wandelt eine LearningUnit in das Format um, das das Frontend erwartet.
+    Wichtig sind:
+    - id
+    - label  (sichtbarer Name)
+    - meta   (Untertitelzeile)
+    - worksheet_files (Liste von Dateinamen)
+    """
+    label = lu.title or "Lerneinheit"
+
+    # Meta-Text: z.B. "Thema: Auge · Klasse: 7a · angelegt am 10.12.2025"
+    meta_parts: List[str] = []
+    if lu.topic:
+        meta_parts.append(f"Thema: {lu.topic}")
+    if lu.grade_level:
+        meta_parts.append(f"Klasse: {lu.grade_level}")
+    created_str = lu.created_at.strftime("%d.%m.%Y")
+    meta_parts.append(f"angelegt am {created_str}")
+
+    meta = " · ".join(meta_parts)
+
+    return {
+        "id": lu.id,
+        "label": label,
+        "meta": meta,
+        "title": lu.title,
+        "topic": lu.topic,
+        "grade_level": lu.grade_level,
+        "language": lu.language,
+        "status": lu.status,
+        "worksheet_files": lu.worksheet_files,
+        "created_at": lu.created_at.isoformat(),
+        "updated_at": lu.updated_at.isoformat(),
+    }
+
+
+# ---------- Endpunkte ----------
+
+
+@router.get("/", response_model=List[Dict[str, Any]])
+def api_list_learning_units():
+    """Alle Lerneinheiten für das Frontend auflisten."""
+    units = list_learning_units()
+    return [unit_to_frontend_dict(u) for u in units]
+
+
+@router.post("/", response_model=Dict[str, Any])
+def api_create_learning_unit(payload: LearningUnitCreatePayload):
+    """
+    Neue Lerneinheit anlegen.
+    Mapped das Frontend-Payload (student/subject/title/grade)
+    auf das generische LearningUnit-Modell.
+    """
+
+    # Mindestens eines der Felder muss gesetzt sein
+    if not (payload.student or payload.subject or payload.title):
+        raise HTTPException(
+            status_code=400,
+            detail="Bitte mindestens Schüler/in, Fach oder Thema angeben.",
+        )
+
+    # Titel/Topic bestimmen
+    # sichtbarer Titel: bevorzugt Thema (title), sonst Kombination
+    if payload.title:
+        title = payload.title
+    else:
+        parts = []
+        if payload.subject:
+            parts.append(payload.subject)
+        if payload.student:
+            parts.append(payload.student)
+        title = " – ".join(parts) if parts else "Lerneinheit"
+
+    topic = payload.title or payload.subject or None
+    grade_level = payload.grade or None
+
+    lu_create = LearningUnitCreate(
+        title=title,
+        description=None,
+        topic=topic,
+        grade_level=grade_level,
+        language="de",
+        worksheet_files=[],
+        status="raw",
+    )
+
+    lu = create_learning_unit(lu_create)
+    return unit_to_frontend_dict(lu)
+
+
+@router.post("/{unit_id}/attach-worksheets", response_model=Dict[str, Any])
+def api_attach_worksheets(unit_id: str, payload: AttachWorksheetsPayload):
+    """
+    Fügt der Lerneinheit eine oder mehrere Arbeitsblätter hinzu.
+    """
+    lu = get_learning_unit(unit_id)
+    if not lu:
+        raise HTTPException(status_code=404, detail="Lerneinheit nicht gefunden.")
+
+    files_to_add = [f for f in payload.worksheet_files if f not in lu.worksheet_files]
+    if files_to_add:
+        new_list = lu.worksheet_files + files_to_add
+        update = LearningUnitUpdate(worksheet_files=new_list)
+        lu = update_learning_unit(unit_id, update)
+        if not lu:
+            raise HTTPException(status_code=500, detail="Lerneinheit konnte nicht aktualisiert werden.")
+
+    return unit_to_frontend_dict(lu)
+
+
+@router.post("/{unit_id}/remove-worksheet", response_model=Dict[str, Any])
+def api_remove_worksheet(unit_id: str, payload: RemoveWorksheetPayload):
+    """
+    Entfernt genau ein Arbeitsblatt aus der Lerneinheit.
+    """
+    lu = get_learning_unit(unit_id)
+    if not lu:
+        raise HTTPException(status_code=404, detail="Lerneinheit nicht gefunden.")
+
+    if payload.worksheet_file not in lu.worksheet_files:
+        # Nichts zu tun, aber kein Fehler – einfach unverändert zurückgeben
+        return unit_to_frontend_dict(lu)
+
+    new_list = [f for f in lu.worksheet_files if f != payload.worksheet_file]
+    update = LearningUnitUpdate(worksheet_files=new_list)
+    lu = update_learning_unit(unit_id, update)
+    if not lu:
+        raise HTTPException(status_code=500, detail="Lerneinheit konnte nicht aktualisiert werden.")
+
+    return unit_to_frontend_dict(lu)
+
+
+@router.delete("/{unit_id}")
+def api_delete_learning_unit(unit_id: str):
+    """
+    Lerneinheit komplett löschen (aktuell vom Frontend noch nicht verwendet).
+    """
+    ok = delete_learning_unit(unit_id)
+    if not ok:
+        raise HTTPException(status_code=404, detail="Lerneinheit nicht gefunden.")
+    return {"status": "deleted", "id": unit_id}
+