feat(selection): expose run sector aggregates and sector filter on results API

- sector_radar: add batch sector-count aggregation and sector member lookup
  over the strict last-good membership snapshot (postgres + in-memory fakes)
- selection: add SelectionSectorReader port, list_sector_counts use case,
  and sector_stock_codes filtering via run identity resolution; queries stay
  inside the selection context per ADR 0001
- http: add GET /api/v1/selection/sectors and forward sector param on
  /results and /runs/{run_id}
- fix stale positional args in pattern-scoring run tests; cover new behavior
  with read-service, application, and HTTP contract tests

zhixing-server/src/zhixing_server/modules/selection/domain/runs.py

@@ -31,6 +31,52 @@ class SelectionResultQuery:
     search: str | None = None
     category: SelectionSignalCategoryFilter | None = None
     sort: SelectionResultSort = "code"
+    sector: str | None = None
+
+
+@dataclass(frozen=True, slots=True)
+class SelectionSectorCount:
+    """One sector and the number of this run's selected stocks it contains."""
+
+    sector_code: str
+    sector_name: str
+    stock_count: int
+
+
+@dataclass(frozen=True, slots=True)
+class SelectionSectorMembership:
+    """Point-in-time sector membership aggregates for a set of stock codes."""
+
+    snapshot_trade_date: date | None
+    sector_counts: tuple[SelectionSectorCount, ...] = ()
+
+
+@dataclass(frozen=True, slots=True)
+class SelectionRunIdentity:
+    """Minimal run locator used to resolve date-dependent filters."""
+
+    run_id: str
+    target_trade_date: date
+
+
+class SelectionSectorReader(Protocol):
+    """Port to the sector-radar context's point-in-time membership reads."""
+
+    def sector_counts(
+        self,
+        stock_codes: Sequence[str],
+        target_trade_date: date,
+        *,
+        sector_type: str = "concept",
+    ) -> SelectionSectorMembership: ...
+
+    def sector_member_codes(
+        self,
+        target_trade_date: date,
+        sector_code: str,
+        *,
+        sector_type: str = "concept",
+    ) -> tuple[str, ...]: ...
 
 
 @dataclass(frozen=True, slots=True)
@@ -139,6 +185,7 @@ class SelectionRunStore(Protocol):
         run_id: str,
         *,
         query: SelectionResultQuery | None = None,
+        sector_stock_codes: Sequence[str] | None = None,
     ) -> SelectionRun | None: ...
 
     def get_latest_run(
@@ -147,8 +194,17 @@ class SelectionRunStore(Protocol):
         target_trade_date: date | None = None,
         *,
         query: SelectionResultQuery | None = None,
+        sector_stock_codes: Sequence[str] | None = None,
     ) -> SelectionRun | None: ...
 
+    def get_run_identity(self, run_id: str) -> SelectionRunIdentity | None: ...
+
+    def get_latest_run_identity(
+        self,
+        strategy: SelectionStrategyName,
+        target_trade_date: date | None = None,
+    ) -> SelectionRunIdentity | None: ...
+
 
 class SelectionUniverseReader(Protocol):
     """Read a qualified market-data source snapshot for one strategy run."""