Issues 19+20: entity-aware schedule import and rollup endpoint

Issue 19:
- entity_id now optional on POST /api/import/schedule
- Resolution: explicit entity_id > name match from row 1 > auto-create
- New params: create_entity_type (default fund), create_vintage_year
- Dry-run reports resolution (will_create/matched/existing)
- Frontend: radio toggle between 'Create from file' and 'Use existing'

Issue 20:
- GET /api/entities/rollup: invested_cents and last_signed_value_cents
  per entity in one pass (SQL aggregates, no waterfall)
- EntitiesList uses rollup instead of N+1 API calls

frontend/src/api.ts

@@ -118,6 +118,17 @@ export const api = {
 
   // Entities
   listEntities: () => request<Entity[]>("/api/entities"),
+  listEntityRollup: () =>
+    request<{
+      id: number;
+      name: string;
+      type: EntityType;
+      vintage_year: number | null;
+      fund_size_cents: number | null;
+      status: EntityStatus;
+      invested_cents: number;
+      last_signed_value_cents: number;
+    }[]>("/api/entities/rollup"),
   getEntity: (id: number) => request<Entity>(`/api/entities/${id}`),
   createEntity: (data: Partial<Entity>) =>
     request<Entity>("/api/entities", { method: "POST", body: JSON.stringify(data) }),