feat: add schema version system with outdated save detection

Introduces a schema version field to GameState. Saves without the
current schema version are flagged on load (showing a modal prompting
reset or proceed), and cloud saves from outdated clients are rejected
server-side. Removes all backfill code now that outdated saves are
handled via the reset flow instead.

New POST /game/reset endpoint creates a fresh save for players who
choose to reset. Save version and current schema version are displayed
in the sidebar below the app version.

packages/types/src/interfaces/Api.ts

@@ -48,6 +48,10 @@ export interface LoadResponse {
   loginBonus: LoginBonusResult | null;
   /** Current login streak (always present) */
   loginStreak: number;
+  /** True when the player's save data is from an older schema version */
+  schemaOutdated: boolean;
+  /** The current expected schema version from the server */
+  currentSchemaVersion: number;
 }
 
 export interface BossChallengeRequest {

packages/types/src/interfaces/GameState.ts

@@ -49,4 +49,6 @@ export interface GameState {
   companions?: CompanionState;
   /** Story chapter unlock and completion state — optional for backwards compatibility */
   story?: StoryState;
+  /** Schema version — used to detect saves from older game versions */
+  schemaVersion?: number;
 }