feat(web): persist game state across page refreshes with resume dialog

- solitaire_wasm: add SolitaireGame::serialize() and from_saved() so JS
  can round-trip the full GameState through localStorage as JSON
- game.js: save {gameState, elapsedSecs, drawThree} to localStorage
  (key: fs_game_save) on every render(); clear the save on win
- game.js: on bootstrap, check for a saved game and show a resume
  dialog if one exists; Resume restores state + timer, New Game discards
  the save and starts fresh with a random seed
- game.html: add #resume-overlay markup (same pattern as win-overlay)
- game.css: add styles for the resume dialog and its secondary button

localStorage failures (private-browsing quota) are silently ignored so
they never block gameplay.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_server/web/game.css

@@ -230,6 +230,68 @@ main {
     pointer-events: none;
 }
 
+/* ── Resume overlay ──────────────────────────────────────────────────── */
+
+#resume-overlay {
+    position: fixed;
+    inset: 0;
+    background: rgba(21, 21, 21, 0.92);
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    z-index: 1000;
+}
+
+#resume-overlay.hidden { display: none; }
+
+.resume-card {
+    background: var(--panel);
+    border: 1px solid rgba(255,255,255,0.12);
+    border-radius: 16px;
+    padding: 40px 48px;
+    text-align: center;
+    display: flex;
+    flex-direction: column;
+    gap: 16px;
+    box-shadow: 0 20px 60px rgba(0,0,0,0.6);
+    max-width: 360px;
+}
+
+.resume-title {
+    font-size: 28px;
+    font-weight: 700;
+    color: var(--accent);
+}
+
+.resume-detail {
+    font-size: 14px;
+    color: var(--text-muted);
+    margin: 0;
+    line-height: 1.5;
+}
+
+.resume-actions {
+    display: flex;
+    gap: 12px;
+    justify-content: center;
+    margin-top: 8px;
+}
+
+.resume-actions button {
+    padding: 12px 24px;
+    font-size: 15px;
+}
+
+.resume-actions button.secondary {
+    background: transparent;
+    border: 1px solid rgba(255,255,255,0.2);
+    color: var(--text-muted);
+}
+
+.resume-actions button.secondary:hover {
+    background: rgba(255,255,255,0.05);
+}
+
 /* ── Win overlay ─────────────────────────────────────────────────────── */
 
 #win-overlay {