feat: add schema version system with outdated save detection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reset or proceed), and cloud saves from outdated clients are rejected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 Removes all backfill code now that outdated saves are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.

apps/web/src/components/game/ClickArea.tsx

@@ -10,7 +10,7 @@ interface FloatText {
 }
 
 export const ClickArea = (): React.JSX.Element => {
-  const { state, handleClick, formatNumber } = useGame();
+  const { state, handleClick, formatNumber, saveSchemaVersion, currentSchemaVersion } = useGame();
   const [floats, setFloats] = useState<FloatText[]>([]);
   const nextIdRef = useRef(0);
 
@@ -41,6 +41,11 @@ export const ClickArea = (): React.JSX.Element => {
     <section className="click-area">
       <h1 className="game-title">Elysium</h1>
       <p className="game-version">v{__WEB_VERSION__}</p>
+      {currentSchemaVersion > 0 && (
+        <p className="game-schema-version">
+          Save: v{saveSchemaVersion} / Latest: v{currentSchemaVersion}
+        </p>
+      )}
       <h2>Guild Hall</h2>
       <div className="click-button-wrapper">
         <button

apps/web/src/components/game/GameLayout.tsx

@@ -13,6 +13,7 @@ import { CodexToast } from "./CodexToast.js";
 import { EditProfileModal } from "./EditProfileModal.js";
 import { EquipmentPanel } from "./EquipmentPanel.js";
 import { OfflineModal } from "./OfflineModal.js";
+import { OutdatedSchemaModal } from "./OutdatedSchemaModal.js";
 import { PrestigePanel } from "./PrestigePanel.js";
 import { ApotheosisPanel } from "./ApotheosisPanel.js";
 import { TranscendencePanel } from "./TranscendencePanel.js";
@@ -52,9 +53,10 @@ const BASE_TABS: { id: Tab; label: string }[] = [
 ];
 
 export const GameLayout = (): React.JSX.Element => {
-  const { state, isLoading, error, battleResult, dismissBattle, lastSavedAt, isSyncing, forceSync, newCodexEntryIds, newStoryChapterIds, loginBonus, dismissLoginBonus } = useGame();
+  const { state, isLoading, error, battleResult, dismissBattle, lastSavedAt, isSyncing, forceSync, newCodexEntryIds, newStoryChapterIds, loginBonus, dismissLoginBonus, schemaOutdated } = useGame();
   const [activeTab, setActiveTab] = useState<Tab>("adventurers");
   const [editingProfile, setEditingProfile] = useState(false);
+  const [dismissedOutdatedWarning, setDismissedOutdatedWarning] = useState(false);
 
   if (isLoading) {
     return (
@@ -91,6 +93,9 @@ export const GameLayout = (): React.JSX.Element => {
         onForceSync={forceSync}
       />
       <OfflineModal />
+      {schemaOutdated && !dismissedOutdatedWarning && (
+        <OutdatedSchemaModal onDismiss={() => { setDismissedOutdatedWarning(true); }} />
+      )}
       <AchievementToast />
       <CodexToast />
       <StoryToast />

apps/web/src/components/game/OutdatedSchemaModal.tsx

@@ -0,0 +1,49 @@
+import { useState } from "react";
+import { useGame } from "../../context/GameContext.js";
+
+interface OutdatedSchemaModalProps {
+  onDismiss: () => void;
+}
+
+export const OutdatedSchemaModal = ({ onDismiss }: OutdatedSchemaModalProps): React.JSX.Element => {
+  const { resetProgress } = useGame();
+  const [isResetting, setIsResetting] = useState(false);
+
+  const handleReset = async (): Promise<void> => {
+    setIsResetting(true);
+    await resetProgress();
+    setIsResetting(false);
+  };
+
+  return (
+    <div className="modal-overlay">
+      <div className="modal offline-modal">
+        <h2>⚠️ Outdated Save Data</h2>
+        <p>
+          Your save data is from an older version of Elysium and may cause bugs or unexpected
+          behaviour. Cloud saves are <strong>disabled</strong> until you reset your progress.
+        </p>
+        <p>
+          Resetting will start you fresh — all progress will be lost.
+        </p>
+        <div className="outdated-modal-actions">
+          <button
+            className="outdated-modal-reset-button"
+            onClick={() => { void handleReset(); }}
+            disabled={isResetting}
+            type="button"
+          >
+            {isResetting ? "Resetting…" : "Reset Progress"}
+          </button>
+          <button
+            className="modal-close-button"
+            onClick={onDismiss}
+            type="button"
+          >
+            Proceed with Bugs
+          </button>
+        </div>
+      </div>
+    </div>
+  );
+};