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.py

@@ -0,0 +1,178 @@
+from __future__ import annotations
+from pydantic import BaseModel, Field
+from typing import List, Dict, Optional
+from pathlib import Path
+from datetime import datetime
+import uuid
+import json
+import threading
+
+# Basisverzeichnis für Arbeitsblätter & Lerneinheiten
+BASE_DIR = Path.home() / "Arbeitsblaetter"
+LEARNING_UNITS_DIR = BASE_DIR / "Lerneinheiten"
+LEARNING_UNITS_FILE = LEARNING_UNITS_DIR / "learning_units.json"
+
+# Thread-Lock, damit Dateizugriffe sicher bleiben
+_lock = threading.Lock()
+
+
+class LearningUnitBase(BaseModel):
+    title: str = Field(..., description="Titel der Lerneinheit, z.B. 'Das Auge – Klasse 7'")
+    description: Optional[str] = Field(None, description="Freitext-Beschreibung")
+    topic: Optional[str] = Field(None, description="Kurz-Thema, z.B. 'Auge'")
+    grade_level: Optional[str] = Field(None, description="Klassenstufe, z.B. '7'")
+    language: Optional[str] = Field("de", description="Hauptsprache der Lerneinheit (z.B. 'de', 'tr')")
+    worksheet_files: List[str] = Field(
+        default_factory=list,
+        description="Liste der zugeordneten Arbeitsblatt-Dateien (Basenames oder Pfade)"
+    )
+    status: str = Field(
+        "raw",
+        description="Pipeline-Status: raw, cleaned, qa_generated, mc_generated, cloze_generated"
+    )
+
+
+class LearningUnitCreate(LearningUnitBase):
+    """Payload zum Erstellen einer neuen Lerneinheit."""
+    pass
+
+
+class LearningUnitUpdate(BaseModel):
+    """Teil-Update für eine Lerneinheit."""
+    title: Optional[str] = None
+    description: Optional[str] = None
+    topic: Optional[str] = None
+    grade_level: Optional[str] = None
+    language: Optional[str] = None
+    worksheet_files: Optional[List[str]] = None
+    status: Optional[str] = None
+
+
+class LearningUnit(LearningUnitBase):
+    id: str
+    created_at: datetime
+    updated_at: datetime
+
+    @classmethod
+    def from_dict(cls, data: Dict) -> "LearningUnit":
+        data = data.copy()
+        if isinstance(data.get("created_at"), str):
+            data["created_at"] = datetime.fromisoformat(data["created_at"])
+        if isinstance(data.get("updated_at"), str):
+            data["updated_at"] = datetime.fromisoformat(data["updated_at"])
+        return cls(**data)
+
+    def to_dict(self) -> Dict:
+        d = self.dict()
+        d["created_at"] = self.created_at.isoformat()
+        d["updated_at"] = self.updated_at.isoformat()
+        return d
+
+
+def _ensure_storage():
+    """Sorgt dafür, dass der Ordner und die JSON-Datei existieren."""
+    LEARNING_UNITS_DIR.mkdir(parents=True, exist_ok=True)
+    if not LEARNING_UNITS_FILE.exists():
+        with LEARNING_UNITS_FILE.open("w", encoding="utf-8") as f:
+            json.dump({}, f)
+
+
+def _load_all_units() -> Dict[str, Dict]:
+    _ensure_storage()
+    with LEARNING_UNITS_FILE.open("r", encoding="utf-8") as f:
+        try:
+            data = json.load(f)
+            if not isinstance(data, dict):
+                return {}
+            return data
+        except json.JSONDecodeError:
+            return {}
+
+
+def _save_all_units(raw: Dict[str, Dict]) -> None:
+    _ensure_storage()
+    with LEARNING_UNITS_FILE.open("w", encoding="utf-8") as f:
+        json.dump(raw, f, ensure_ascii=False, indent=2)
+
+
+def list_learning_units() -> List[LearningUnit]:
+    with _lock:
+        raw = _load_all_units()
+        return [LearningUnit.from_dict(v) for v in raw.values()]
+
+
+def get_learning_unit(unit_id: str) -> Optional[LearningUnit]:
+    with _lock:
+        raw = _load_all_units()
+        data = raw.get(unit_id)
+        if not data:
+            return None
+        return LearningUnit.from_dict(data)
+
+
+def create_learning_unit(payload: LearningUnitCreate) -> LearningUnit:
+    now = datetime.utcnow()
+    lu = LearningUnit(
+        id=str(uuid.uuid4()),
+        created_at=now,
+        updated_at=now,
+        **payload.dict()
+    )
+    with _lock:
+        raw = _load_all_units()
+        raw[lu.id] = lu.to_dict()
+        _save_all_units(raw)
+    return lu
+
+
+def update_learning_unit(unit_id: str, payload: LearningUnitUpdate) -> Optional[LearningUnit]:
+    with _lock:
+        raw = _load_all_units()
+        existing = raw.get(unit_id)
+        if not existing:
+            return None
+
+        lu = LearningUnit.from_dict(existing)
+        update_data = payload.dict(exclude_unset=True)
+
+        for field, value in update_data.items():
+            setattr(lu, field, value)
+
+        lu.updated_at = datetime.utcnow()
+        raw[lu.id] = lu.to_dict()
+        _save_all_units(raw)
+        return lu
+
+
+def delete_learning_unit(unit_id: str) -> bool:
+    with _lock:
+        raw = _load_all_units()
+        if unit_id not in raw:
+            return False
+        del raw[unit_id]
+        _save_all_units(raw)
+        return True
+
+
+def attach_worksheets(unit_id: str, worksheet_files: List[str]) -> Optional[LearningUnit]:
+    """
+    Hängt eine Liste von Arbeitsblatt-Dateien an eine bestehende Lerneinheit an.
+    Doppelte Einträge werden vermieden.
+    """
+    with _lock:
+        raw = _load_all_units()
+        existing = raw.get(unit_id)
+        if not existing:
+            return None
+
+        lu = LearningUnit.from_dict(existing)
+        current_set = set(lu.worksheet_files)
+        for f in worksheet_files:
+            current_set.add(f)
+        lu.worksheet_files = sorted(current_set)
+        lu.updated_at = datetime.utcnow()
+
+        raw[lu.id] = lu.to_dict()
+        _save_all_units(raw)
+        return lu
+