feat: external precedent library with auto halacha extraction

Adds a third corpus of legal authority distinct from style_corpus
(Daphna's prior decisions for voice) and case_precedents (chair-attached
quotes per case). The new corpus holds chair-uploaded court rulings and
other appeals committee decisions, with binding rules (הלכות) extracted
automatically and queued for chair approval.

Pipeline (web/app.py + services/precedent_library.py):
file → extract → chunk → Voyage embed → halacha_extractor → store +
publish progress over the existing Redis SSE channel.

Schema V7 (services/db.py): extends case_law with source_kind +
extraction status fields under a CHECK constraint pinning practice_area
to the three appeals committee domains (rishuy_uvniya, betterment_levy,
compensation_197). New precedent_chunks (vector(1024)) and halachot
tables (vector(1024) over rule_statement, IVFFlat indexes, gin on
practice_areas/subject_tags). Halachot start as pending_review; only
approved/published rows are visible to search_precedent_library.

Agents: legal-writer, legal-researcher, legal-analyst, legal-ceo,
legal-qa get search_precedent_library. legal-writer prompt explains
the three-corpus distinction and CREAC use; legal-qa now verifies that
every cited halacha resolves to an approved row in the corpus.

UI: /precedents page with four tabs — library / semantic search /
pending review (J/K nav, A/R/E shortcuts, badge count) / stats.
Reuses the existing upload-sheet progress + SSE pattern.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

mcp-server/src/legal_mcp/services/chunker.py

@@ -7,14 +7,16 @@ from dataclasses import dataclass, field
 
 from legal_mcp import config
 
-# Hebrew legal section headers
+# Hebrew legal section headers.
+# Covers both appeals committee decisions and external court rulings —
+# court rulings use slightly different vocabulary (פסק דין, נימוקים, סוף דבר).
 SECTION_PATTERNS = [
     (r"רקע\s*עובדתי|רקע\s*כללי|העובדות|הרקע", "facts"),
     (r"טענות\s*העוררי[םן]|טענות\s*המערערי[םן]|עיקר\s*טענות\s*העוררי[םן]", "appellant_claims"),
     (r"טענות\s*המשיבי[םן]|תשובת\s*המשיבי[םן]|עיקר\s*טענות\s*המשיבי[םן]", "respondent_claims"),
-    (r"דיון\s*והכרעה|דיון|הכרעה|ניתוח\s*משפטי|המסגרת\s*המשפטית", "legal_analysis"),
-    (r"מסקנ[הות]|סיכום", "conclusion"),
-    (r"החלטה|לפיכך\s*אני\s*מחליט|התוצאה", "ruling"),
+    (r"דיון\s*והכרעה|דיון|הכרעה|ניתוח\s*משפטי|המסגרת\s*המשפטית|נימוקים", "legal_analysis"),
+    (r"מסקנ[הות]|סיכום|סוף\s*דבר", "conclusion"),
+    (r"פסק[- ]?דין|החלטה|לפיכך\s*אני\s*מחליט|התוצאה", "ruling"),
     (r"מבוא|פתיחה|לפניי", "intro"),
 ]