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>

klausur-service/backend/models/grading.py

@@ -0,0 +1,71 @@
+"""
+Klausur-Service Grading Models
+
+Grade thresholds, labels, criteria, and audit logging.
+"""
+
+from dataclasses import dataclass
+from datetime import datetime
+from typing import Optional, Dict, Any
+
+
+# =============================================
+# GRADE CONSTANTS
+# =============================================
+
+GRADE_THRESHOLDS = {
+    15: 95, 14: 90, 13: 85, 12: 80, 11: 75, 10: 70,
+    9: 65, 8: 60, 7: 55, 6: 50, 5: 45, 4: 40,
+    3: 33, 2: 27, 1: 20, 0: 0
+}
+
+GRADE_LABELS = {
+    15: "1+ (sehr gut plus)", 14: "1 (sehr gut)", 13: "1- (sehr gut minus)",
+    12: "2+ (gut plus)", 11: "2 (gut)", 10: "2- (gut minus)",
+    9: "3+ (befriedigend plus)", 8: "3 (befriedigend)", 7: "3- (befriedigend minus)",
+    6: "4+ (ausreichend plus)", 5: "4 (ausreichend)", 4: "4- (ausreichend minus)",
+    3: "5+ (mangelhaft plus)", 2: "5 (mangelhaft)", 1: "5- (mangelhaft minus)",
+    0: "6 (ungenuegend)"
+}
+
+DEFAULT_CRITERIA = {
+    "rechtschreibung": {"weight": 0.15, "label": "Rechtschreibung"},
+    "grammatik": {"weight": 0.15, "label": "Grammatik"},
+    "inhalt": {"weight": 0.40, "label": "Inhalt"},
+    "struktur": {"weight": 0.15, "label": "Struktur"},
+    "stil": {"weight": 0.15, "label": "Stil"},
+}
+
+
+# =============================================
+# AUDIT LOG
+# =============================================
+
+@dataclass
+class AuditLogEntry:
+    """Audit log entry for tracking changes."""
+    id: str
+    timestamp: datetime
+    user_id: str
+    action: str  # score_update, gutachten_update, status_change, examiner_assign
+    entity_type: str  # klausur, student
+    entity_id: str
+    field: Optional[str]
+    old_value: Optional[str]
+    new_value: Optional[str]
+    details: Optional[Dict]
+
+    def to_dict(self) -> Dict[str, Any]:
+        """Convert to dictionary for JSON serialization."""
+        return {
+            'id': self.id,
+            'timestamp': self.timestamp.isoformat(),
+            'user_id': self.user_id,
+            'action': self.action,
+            'entity_type': self.entity_type,
+            'entity_id': self.entity_id,
+            'field': self.field,
+            'old_value': self.old_value,
+            'new_value': self.new_value,
+            'details': self.details
+        }