Add game selection screen and new run wizard

Build a 3-step wizard at /runs/new: select game (themed gradient cards
grouped by generation with filter tabs), configure rules (reuses existing
RulesConfiguration), and name/create run. Remove standalone Games and Rules
pages since they're now integrated into the wizard flow.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/pages/index.ts

@@ -1,5 +1,4 @@
 export { Home } from './Home'
-export { GameSelect } from './GameSelect'
+export { NewRun } from './NewRun'
 export { Dashboard } from './Dashboard'
 export { Encounters } from './Encounters'
-export { Rules } from './Rules'