feat(engine): add weekly goals with ISO-week rollover and +75 XP bonus

Phase 6 part 2b:
- solitaire_data::weekly defines WeeklyGoalKind, WeeklyGoalDef,
  WeeklyGoalContext, current_iso_week_key, and three starter goals
  (5 wins, 3 no-undo wins, 3 fast wins).
- PlayerProgress gains weekly_goal_week_iso, roll_weekly_goals_if_new_week,
  and record_weekly_progress (returns true exactly once per goal completion).
- WeeklyGoalsPlugin evaluates GameWonEvent against WEEKLY_GOALS, rolls the
  week if needed, increments matching counters, awards WEEKLY_GOAL_XP for
  newly-completed goals, persists progress, and fires
  WeeklyGoalCompletedEvent.

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

solitaire_engine/src/lib.rs

@@ -12,12 +12,14 @@ pub mod progress_plugin;
 pub mod resources;
 pub mod stats_plugin;
 pub mod table_plugin;
+pub mod weekly_goals_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 weekly_goals_plugin::{WeeklyGoalCompletedEvent, WeeklyGoalsPlugin};
 pub use animation_plugin::{AnimationPlugin, CardAnim};
 pub use card_plugin::{CardEntity, CardLabel, CardPlugin};
 pub use events::{