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/card_plugin.rs

@@ -41,7 +41,9 @@ use crate::ui_theme::{
 };
 
 /// Fraction of card height used as vertical offset between face-up tableau cards.
-pub const TABLEAU_FAN_FRAC: f32 = 0.25;
+/// Must match `layout::TABLEAU_FAN_FRAC` so the initial layout and the first
+/// dynamic update from `update_tableau_fan_frac` produce identical spacing.
+pub const TABLEAU_FAN_FRAC: f32 = 0.18;
 
 /// Per-card vertical step for face-down tableau cards, as a fraction of
 /// card height. Smaller than [`TABLEAU_FAN_FRAC`] because face-down cards
@@ -51,11 +53,11 @@ pub const TABLEAU_FAN_FRAC: f32 = 0.25;
 /// renderer creates a visible offset between the card face and where
 /// clicks land.
 ///
-/// Matches `layout::TABLEAU_FACEDOWN_FAN_FRAC` (0.20). Both constants must
+/// Matches `layout::TABLEAU_FACEDOWN_FAN_FRAC` (0.14). Both constants must
 /// stay in sync; the layout constant drives the adaptive LayoutResource value
 /// used at runtime, while this one is the minimum floor used by
 /// `update_tableau_fan_frac` when computing proportional updates.
-pub const TABLEAU_FACEDOWN_FAN_FRAC: f32 = 0.20;
+pub const TABLEAU_FACEDOWN_FAN_FRAC: f32 = 0.14;
 
 /// Fraction of card height used as a tiny offset between stacked cards in
 /// non-tableau piles, so stacking is visible. Public so other plugins