feat: remove a saved game & redirect on missing/deleted game (#20)

- DELETE /api/games/:id route + Db.delete() (404 when absent)
- PresetPicker: per-saved-game trash button + confirm dialog (Cancel/Delete)
- App: runDeleteGame; useSse onError -> goHome on 'deleted'/'not found'
  (a deleted/missing game now returns the live tab and any deep link home)
- DeleteGameResponse in shared/protocol.ts; api.deleteGame()
- unit test (Db.delete) + 2 e2e tests (home-screen delete; in-flight delete
  returns the active tab home and a fresh deep link lands on home)
- version 0.7.0 -> 0.8.0 + changelog

Fixes #20

shared/protocol.ts

@@ -141,6 +141,11 @@ export interface GameSummary {
   date: string;
 }
 
+/** Response for deleting a saved game (see `DELETE /api/games/:id`). */
+export interface DeleteGameResponse {
+  deleted: boolean;
+}
+
 /**
  * Deterministic, stable per-nation color for the choropleth. Hashes the nation id
  * to a hue; sat/light tuned for the dark command-center theme. Pure + shared so