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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "history",
-  "version": "0.7.0",
+  "version": "0.8.0",
   "private": true,
   "type": "module",
   "description": "AI-driven alternate-history simulator — the LLM is the world engine (Pax Historia style).",