fix(multi): resolve 14 bugs from second comprehensive review

Core (solitaire_core):
- fix(scoring): apply -15 penalty for Foundation→Tableau moves when
  take_from_foundation is enabled; update test
- fix(solver): is_won() validates full Ace→King suit sequence, not
  just card count — prevents hint system from emitting invalid paths

Engine — animation / layout:
- fix(animation): guard CardAnim advance against duration=0 to prevent
  NaN-poisoned Transform (analogous to CardAnimation's instant-snap path)
- fix(card_plugin): align TABLEAU_FAN_FRAC (0.25→0.18) and
  TABLEAU_FACEDOWN_FAN_FRAC (0.20→0.14) with layout.rs so the initial
  layout and first dynamic update produce identical fan spacing
- fix(layout): update tableau_fan_frac doc comment from 0.25→0.18

Engine — ECS / modal guards:
- fix(auto_complete): drive_auto_complete now checks PausedResource so
  cooldown does not tick while paused (prevents instant-move on unpause)
- fix(play_by_seed): handle_open_dialog checks global ModalScrim guard
  to prevent stacking over an existing modal
- fix(win_summary): spawn_win_summary_after_delay checks global
  ModalScrim guard; collect_session_achievements uses .next() not
  .last() to avoid draining the new_games stream

Engine — message registration:
- fix(leaderboard): register InfoToastEvent in LeaderboardPlugin::build
  so opt-in/opt-out toasts work under MinimalPlugins
- fix(replay_playback): register StateChangedEvent in
  ReplayPlaybackPlugin::build to prevent panic when used standalone

Security:
- fix(sync_setup): zero password SyncFieldBuffer immediately after
  spawning auth task — credential must not linger in ECS components

Server:
- fix(auth): replace MIME contains-chain with exact match for avatar
  upload; removes illusory starts_with guard and dead ALLOWED_IMAGE_TYPES

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

solitaire_engine/src/win_summary_plugin.rs

@@ -508,7 +508,7 @@ fn collect_session_achievements(
 ) {
     // Reset on any new-game request (including mode switches via Z/X/C/T) so
     // achievements from the previous session are not carried into the next one.
-    if new_games.read().last().is_some() {
+    if new_games.read().next().is_some() {
         session.names.clear();
     }
     for ev in unlocks.read() {
@@ -539,6 +539,7 @@ fn spawn_win_summary_after_delay(
     settings: Option<Res<SettingsResource>>,
     time: Res<Time>,
     overlays: Query<Entity, With<WinSummaryOverlay>>,
+    other_scrims: Query<(), (With<ModalScrim>, Without<WinSummaryOverlay>)>,
     mut delay: Local<Option<f32>>,
 ) {
     // Process new win events.
@@ -569,8 +570,8 @@ fn spawn_win_summary_after_delay(
         *remaining -= time.delta_secs();
         if *remaining <= 0.0 {
             *delay = None;
-            // Only spawn if there is no overlay already.
-            if overlays.is_empty() {
+            // Only spawn if no overlay of any kind is already visible.
+            if overlays.is_empty() && other_scrims.is_empty() {
                 // Drain any XpAwardedEvents that arrived this frame but were
                 // not yet consumed by `cache_win_data` (which may run later in
                 // the same schedule).  Accumulating here ensures the modal