fix(multi): resolve 26 bugs found in comprehensive codebase review

Core fixes (issues #12, #13, #22):
- #12: undo now preserves score delta instead of restoring snapshot score
- #13: take_from_foundation defaults to false (non-standard house rule)
- #22: check_win validates full suit sequence, not just card count

Engine fixes:
- #8:  replay keyboard input guard against non-replay state
- #9:  help modal scrims.is_empty() guard added
- #10: settings modal scrims.is_empty() guard added
- #11: sync_plugin builds payload at poll time (not task-spawn time)
- #14: server replay mode case-sensitivity fix ("Classic")
- #15: play_by_seed_plugin confirmed flag set to true on launch
- #16: replay back-step debounce via Local<bool> + StateChangedEvent;
       register StateChangedEvent in ReplayOverlayPlugin (fixes 52 tests)
- #17: time-attack timer ignores win-summary overlay
- #18: HUD dropdown glyphs U+25BE → U+2193 (FiraMono-safe arrow)
- #19: theme plugin applies immediate visual update on A→B→A switch
- #20: SyncAuthError / SyncBusyOverlay split into separate entities so
       auth errors are visible after busy overlay is hidden
- #21: handle_forfeit ordered before update_stats_on_new_game
- #23: server merge uses correct avg_time_seconds and games_lost math
- #24: win_summary migrated to ModalScrim pattern
- #25: card_animation apply_deferred between animation systems
- #26: cursor_plugin HashMap access uses .get() with fallback
- #27: auto_complete mid-sequence deactivation guard
- #28: feedback_anim SettleAnim ordered before FoundationFlourish
- #29: achievement_plugin iterates all win events; adds scrims guard
- #30: leaderboard modal scrims.is_empty() guard added
- #31: server auth tmp file cleanup on rename failure
- #32: sync_setup modal scrims.is_empty() guard added
- #33: font_plugin uses match fallback; TokioRuntimeResource graceful
       current-thread fallback on runtime init failure

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

solitaire_server/src/auth.rs

@@ -390,7 +390,10 @@ pub async fn upload_avatar(
     // Write to a temp file then atomically rename so concurrent readers never
     // see a partially-written avatar.
     std::fs::write(&tmp_path, &body).map_err(|e| AppError::Internal(e.to_string()))?;
-    std::fs::rename(&tmp_path, &path).map_err(|e| AppError::Internal(e.to_string()))?;
+    if let Err(e) = std::fs::rename(&tmp_path, &path) {
+        let _ = std::fs::remove_file(&tmp_path);
+        return Err(AppError::Internal(e.to_string()));
+    }
     // Remove stale files with other extensions after the atomic rename.
     for old_ext in &["jpg", "png", "webp", "gif"] {
         if *old_ext != ext {

solitaire_server/src/replays.rs

@@ -35,7 +35,7 @@ use crate::{error::AppError, middleware::AuthenticatedUser, AppState};
 /// the desktop client's transitive dependencies.
 #[derive(Debug, Deserialize)]
 struct ReplayHeader {
-    seed: i64,
+    seed: u64,
     draw_mode: String,
     mode: String,
     time_seconds: i64,
@@ -94,6 +94,9 @@ pub async fn upload(
     let id = Uuid::new_v4().to_string();
     let received_at = Utc::now().to_rfc3339();
     let replay_json = serde_json::to_string(&payload)?;
+    // SQLite INTEGER columns bind as i64. Reinterpret the u64 bits — the
+    // database stores the same 8 bytes; high-bit seeds round-trip correctly.
+    let seed_i64 = header.seed as i64;
 
     sqlx::query!(
         r#"INSERT INTO replays (
@@ -102,7 +105,7 @@ pub async fn upload(
            ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)"#,
         id,
         user.user_id,
-        header.seed,
+        seed_i64,
         header.draw_mode,
         header.mode,
         header.time_seconds,
@@ -116,7 +119,7 @@ pub async fn upload(
 
     // Update leaderboard best score/time for opted-in users when this replay
     // beats their existing best. Only classic mode counts for the leaderboard.
-    if header.mode == "classic" {
+    if header.mode == "Classic" {
         sqlx::query!(
             r#"UPDATE leaderboard
                SET best_score      = ?,