feat(engine): add daily challenge, level-up toast, and daily_devotee achievement

Phase 6 part 2 (partial):
- daily_seed_for(date) and PlayerProgress::record_daily_completion in
  solitaire_data, with streak logic that increments on consecutive days,
  resets on a skipped day, and is idempotent on same-day re-completions.
- DailyChallengePlugin tracks today's seed, awards +100 XP and updates
  the streak when the player wins a game whose seed matches. Pressing C
  starts a new game with the daily seed.
- LevelUpEvent toast in AnimationPlugin announces level changes.
- AchievementContext gains daily_challenge_streak; daily_devotee
  achievement unlocks at streak >= 7. AchievementPlugin reads
  ProgressResource and runs after ProgressUpdate.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

solitaire_engine/src/lib.rs

@@ -3,6 +3,7 @@
 pub mod achievement_plugin;
 pub mod animation_plugin;
 pub mod card_plugin;
+pub mod daily_challenge_plugin;
 pub mod events;
 pub mod game_plugin;
 pub mod input_plugin;
@@ -13,6 +14,9 @@ pub mod stats_plugin;
 pub mod table_plugin;
 
 pub use achievement_plugin::{AchievementPlugin, AchievementsResource};
+pub use daily_challenge_plugin::{
+    DailyChallengeCompletedEvent, DailyChallengePlugin, DailyChallengeResource,
+};
 pub use progress_plugin::{LevelUpEvent, ProgressPlugin, ProgressResource, ProgressUpdate};
 pub use animation_plugin::{AnimationPlugin, CardAnim};
 pub use card_plugin::{CardEntity, CardLabel, CardPlugin};