feat: link related precedents across court instances (SCHEMA_V11)

Add ability to mark case_law records as related (e.g. same appeal
through ועדת ערר → מנהלי → עליון):
- DB: case_law_relations join table (bidirectional, V11 migration)
- DB CRUD: add/remove/get_case_law_relations
- Service: get_precedent() now returns related_cases[]
- MCP: precedent_link_cases + precedent_unlink_cases tools
- REST: POST/DELETE /api/precedent-library/{id}/relations
- UI: RelatedCasesSection on detail page with search dialog and unlink

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

mcp-server/src/legal_mcp/tools/precedent_library.py

@@ -116,6 +116,54 @@ async def precedent_library_get(case_law_id: str) -> str:
     return _ok(record)
 
 
+async def precedent_link_cases(
+    case_law_id_a: str,
+    case_law_id_b: str,
+    relation_type: str = "same_case_chain",
+) -> str:
+    """קישור שתי פסיקות כקשורות זו לזו (דו-כיווני). idempotent.
+
+    Args:
+        case_law_id_a: UUID של פסיקה ראשונה.
+        case_law_id_b: UUID של פסיקה שנייה.
+        relation_type: same_case_chain | overruled_by | distinguished
+    """
+    try:
+        a = UUID(case_law_id_a)
+        b = UUID(case_law_id_b)
+    except ValueError:
+        return _err("case_law_id לא תקין")
+    rec_a = await db.get_case_law(a)
+    rec_b = await db.get_case_law(b)
+    if not rec_a:
+        return _err(f"פסיקה {case_law_id_a} לא נמצאה")
+    if not rec_b:
+        return _err(f"פסיקה {case_law_id_b} לא נמצאה")
+    await db.add_case_law_relation(a, b, relation_type)
+    return _ok({
+        "linked": True,
+        "relation_type": relation_type,
+        "a": {"id": case_law_id_a, "case_number": rec_a.get("case_number"), "court": rec_a.get("court")},
+        "b": {"id": case_law_id_b, "case_number": rec_b.get("case_number"), "court": rec_b.get("court")},
+    })
+
+
+async def precedent_unlink_cases(case_law_id_a: str, case_law_id_b: str) -> str:
+    """הסרת קישור בין שתי פסיקות (דו-כיווני).
+
+    Args:
+        case_law_id_a: UUID של פסיקה ראשונה.
+        case_law_id_b: UUID של פסיקה שנייה.
+    """
+    try:
+        a = UUID(case_law_id_a)
+        b = UUID(case_law_id_b)
+    except ValueError:
+        return _err("case_law_id לא תקין")
+    await db.remove_case_law_relation(a, b)
+    return _ok({"unlinked": True, "a": case_law_id_a, "b": case_law_id_b})
+
+
 async def precedent_library_delete(case_law_id: str) -> str:
     """מחיקת פסיקה מהקורפוס. cascade: chunks + halachot."""
     try: