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/services/db.py

@@ -700,6 +700,20 @@ CREATE INDEX IF NOT EXISTS idx_case_law_chair ON case_law(chair_name) WHERE chai
 CREATE INDEX IF NOT EXISTS idx_case_law_district ON case_law(district) WHERE district <> '';
 """
 
+SCHEMA_V11_SQL = """
+CREATE TABLE IF NOT EXISTS case_law_relations (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    case_law_id UUID NOT NULL REFERENCES case_law(id) ON DELETE CASCADE,
+    related_id   UUID NOT NULL REFERENCES case_law(id) ON DELETE CASCADE,
+    relation_type TEXT NOT NULL DEFAULT 'same_case_chain',
+    created_at TIMESTAMPTZ DEFAULT now(),
+    UNIQUE(case_law_id, related_id),
+    CHECK (case_law_id <> related_id)
+);
+CREATE INDEX IF NOT EXISTS idx_clr_a ON case_law_relations(case_law_id);
+CREATE INDEX IF NOT EXISTS idx_clr_b ON case_law_relations(related_id);
+"""
+
 
 async def _run_schema_migrations(pool: asyncpg.Pool) -> None:
     async with pool.acquire() as conn:
@@ -714,7 +728,8 @@ async def _run_schema_migrations(pool: asyncpg.Pool) -> None:
         await conn.execute(SCHEMA_V8_SQL)
         await conn.execute(SCHEMA_V9_SQL)
         await conn.execute(SCHEMA_V10_SQL)
-    logger.info("Database schema initialized (v1-v10)")
+        await conn.execute(SCHEMA_V11_SQL)
+    logger.info("Database schema initialized (v1-v11)")
 
 
 async def init_schema() -> None:
@@ -1735,6 +1750,59 @@ async def get_case_law(case_law_id: UUID) -> dict | None:
     return _row_to_case_law(row) if row else None
 
 
+async def add_case_law_relation(
+    a_id: UUID, b_id: UUID, relation_type: str = "same_case_chain"
+) -> None:
+    """Link two case_law records bidirectionally. Idempotent (ON CONFLICT DO NOTHING)."""
+    pool = await get_pool()
+    async with pool.acquire() as conn:
+        await conn.executemany(
+            """
+            INSERT INTO case_law_relations(case_law_id, related_id, relation_type)
+            VALUES($1, $2, $3)
+            ON CONFLICT (case_law_id, related_id) DO NOTHING
+            """,
+            [(a_id, b_id, relation_type), (b_id, a_id, relation_type)],
+        )
+
+
+async def remove_case_law_relation(a_id: UUID, b_id: UUID) -> None:
+    """Remove a bidirectional link between two case_law records."""
+    pool = await get_pool()
+    await pool.execute(
+        """
+        DELETE FROM case_law_relations
+        WHERE (case_law_id = $1 AND related_id = $2)
+           OR (case_law_id = $2 AND related_id = $1)
+        """,
+        a_id,
+        b_id,
+    )
+
+
+async def get_case_law_relations(case_law_id: UUID) -> list[dict]:
+    """Return all case_law records linked to case_law_id, ordered by date asc."""
+    pool = await get_pool()
+    rows = await pool.fetch(
+        """
+        SELECT cl.*, r.relation_type
+        FROM case_law_relations r
+        JOIN case_law cl ON cl.id = r.related_id
+        WHERE r.case_law_id = $1
+        ORDER BY cl.date ASC NULLS LAST
+        """,
+        case_law_id,
+    )
+    results = []
+    for row in rows:
+        d = dict(row)
+        relation_type = d.pop("relation_type")
+        normalized = _row_to_case_law(d)
+        normalized["relation_type"] = relation_type
+        results.append(normalized)
+    return results
+
+
 async def get_case_law_by_citation(case_number: str) -> dict | None:
     pool = await get_pool()
     row = await pool.fetchrow(