feat: Add 76 Level-2 regex checks for document correctness verification

Split dsi_document_checker.py (466 LOC) into doc_checks/ package (9 files).
Two-pass L1→L2 logic: L1 checks "Is it mentioned?", L2 checks "Is it correct?"
(e.g. controller has full address, specific Art. 6 lit., concrete time periods).

138 total checks (62 L1 + 76 L2) across 7 doc types:
- DSE Art. 13: 31, Impressum §5 TMG: 16, Cookie §25 TDDDG: 15
- Widerruf §355: 15, AGB §305ff: 21, Social Media Art. 26: 20, DSFA Art. 35: 18

Frontend: hierarchical L1→L2 display with dual progress bars
(green=completeness, blue=correctness).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend-compliance/compliance/services/doc_checks/__init__.py

@@ -0,0 +1,32 @@
+"""
+doc_checks — Legal document compliance checkers.
+
+Provides checklists and functions for verifying legal documents
+(DSI, AGB, Impressum, Cookie, Widerruf, Social Media, DSFA)
+against their mandatory content requirements.
+
+Two check levels:
+  L1 — "Is the mandatory field mentioned?"
+  L2 — "Is it correct/complete?"
+"""
+
+from .runner import check_document_completeness, classify_document_type
+from .dse_checks import ART13_CHECKLIST
+from .widerruf_checks import WIDERRUF_CHECKLIST
+from .agb_checks import AGB_CHECKLIST
+from .impressum_checks import IMPRESSUM_CHECKLIST
+from .cookie_checks import COOKIE_CHECKLIST
+from .social_media_checks import JOINT_CONTROLLER_CHECKLIST
+from .dsfa_checks import DSFA_CHECKLIST
+
+__all__ = [
+    "check_document_completeness",
+    "classify_document_type",
+    "ART13_CHECKLIST",
+    "WIDERRUF_CHECKLIST",
+    "AGB_CHECKLIST",
+    "IMPRESSUM_CHECKLIST",
+    "COOKIE_CHECKLIST",
+    "JOINT_CONTROLLER_CHECKLIST",
+    "DSFA_CHECKLIST",
+]