feat(settings): time-bonus multiplier slider in Settings → Gameplay

Cosmetic-only player setting (default 1.0, range 0.0-2.0, step 0.1)
that scales the time-bonus row shown in the win-summary modal's
score breakdown. Achievement thresholds, lifetime score totals, and
leaderboard submissions still use the raw values produced by
`solitaire_core::scoring`, so the multiplier never affects what gets
recorded — just what the player sees on the win screen.

- New `Settings::time_bonus_multiplier` field with `#[serde(default)]`
  + `sanitized()` clamp so older settings.json files load cleanly.
- New constants `TIME_BONUS_MULTIPLIER_{MIN,MAX,STEP}` re-exported
  through `solitaire_data::lib`.
- `settings_plugin` adds a slider row under the Gameplay header
  matching the existing tooltip-delay control.
- `win_summary_plugin` applies the multiplier when rendering the
  time-bonus row of the score breakdown; "Off" label when 0.0.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

solitaire_data/src/lib.rs

@@ -141,7 +141,9 @@ pub use challenge::{challenge_count, challenge_seed_for, CHALLENGE_SEEDS};
 pub mod settings;
 pub use settings::{
     load_settings_from, save_settings_to, settings_file_path, AnimSpeed, Settings, SyncBackend,
-    Theme, WindowGeometry, TOOLTIP_DELAY_MAX_SECS, TOOLTIP_DELAY_MIN_SECS, TOOLTIP_DELAY_STEP_SECS,
+    Theme, WindowGeometry, TIME_BONUS_MULTIPLIER_MAX, TIME_BONUS_MULTIPLIER_MIN,
+    TIME_BONUS_MULTIPLIER_STEP, TOOLTIP_DELAY_MAX_SECS, TOOLTIP_DELAY_MIN_SECS,
+    TOOLTIP_DELAY_STEP_SECS,
 };
 
 pub mod auth_tokens;