fix+refactor+docs: P0–P3 todo list items

P0 fixes:
- Register WinSummaryPlugin, SelectionPlugin, CardAnimationPlugin in main.rs
  (all three were exported but never wired — features silently did nothing)
- game_state::draw(): increment move_count on waste→stock recycle, not just
  on normal draws; add move_count_increments_on_recycle regression test

P1 fixes:
- solitaire_server/Cargo.toml: remove duplicate dev-dependencies
  (solitaire_sync, uuid, chrono, jsonwebtoken were in both sections)

P2 — input_plugin refactor:
- Split 198-line handle_keyboard() into three focused systems under 110 lines each:
  handle_keyboard_core (U/N/Z/D/Space), handle_keyboard_hint (H), handle_keyboard_forfeit (G)
- Introduce KeyboardConfirmState resource to share countdown timers across systems
- Add three new unit tests: all_hints_suggests_draw_*, all_hints_is_empty_when_truly_stuck,
  new_game_confirm_window_is_positive

P2 — achievement predicate tests (solitaire_core):
- Add 10 direct unit tests for speed_demon, lightning, no_undo, high_scorer,
  on_a_roll, comeback predicates (previously only covered via check_achievements())
- 141 core tests now passing

P2 — server tests:
- solitaire_server/src/sync.rs: 4 unit tests for merge logic (no DB required)
- solitaire_server/src/leaderboard.rs: 2 unit tests for entry shape and sort order

P3 — documentation:
- Add struct-level ///  to 12 Plugin structs (ChallengePlugin, CursorPlugin,
  AnimationPlugin, HelpPlugin, PausePlugin, AudioPlugin, DailyChallengePlugin,
  HudPlugin, LeaderboardPlugin, OnboardingPlugin, TimeAttackPlugin, WeeklyGoalsPlugin)
- Add field-level /// to Card, Pile, Deck, GameState, AchievementContext, AchievementDef
- Add /// to WeeklyGoalKind, WeeklyGoalDef, WeeklyGoalContext, StatsExt::update_on_win

card_animation module (new files from previous session):
- chain.rs, diagnostics.rs, tuning.rs, updated interaction.rs/animation.rs/mod.rs/lib.rs
- Remove unused HOVER_SCALE_DEFAULT / DRAG_LIFT_SCALE_DEFAULT / HOVER_LERP_SPEED_DEFAULT constants
- Add handle_touch_stock_tap so touch users can draw from the stock pile

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

solitaire_server/src/sync.rs

@@ -220,3 +220,118 @@ async fn update_leaderboard_if_opted_in(
 
     Ok(())
 }
+
+// ---------------------------------------------------------------------------
+// Tests — pure merge logic; no database required
+// ---------------------------------------------------------------------------
+
+#[cfg(test)]
+mod tests {
+    use chrono::Utc;
+    use solitaire_sync::{AchievementRecord, PlayerProgress, StatsSnapshot, SyncPayload, merge};
+    use uuid::Uuid;
+
+    /// Build a minimal `SyncPayload` with default fields, overridden by the
+    /// caller as needed. Using `Uuid::nil()` keeps every test self-contained.
+    fn make_payload(stats: StatsSnapshot, achievements: Vec<AchievementRecord>) -> SyncPayload {
+        SyncPayload {
+            user_id: Uuid::nil(),
+            stats,
+            achievements,
+            progress: PlayerProgress::default(),
+            last_modified: Utc::now(),
+        }
+    }
+
+    fn default_payload() -> SyncPayload {
+        make_payload(StatsSnapshot::default(), vec![])
+    }
+
+    // -----------------------------------------------------------------------
+    // 1. Merge keeps the higher games_played from the remote side.
+    // -----------------------------------------------------------------------
+
+    #[test]
+    fn sync_merge_keeps_higher_games_played() {
+        let mut local = default_payload();
+        local.stats.games_played = 10;
+
+        let mut remote = default_payload();
+        remote.stats.games_played = 25; // remote is ahead
+
+        let (merged, _) = merge(&local, &remote);
+        assert_eq!(
+            merged.stats.games_played, 25,
+            "merge must keep the higher games_played value from remote"
+        );
+    }
+
+    // -----------------------------------------------------------------------
+    // 2. Merge keeps the higher best_single_score from the local side.
+    // -----------------------------------------------------------------------
+
+    #[test]
+    fn sync_merge_keeps_best_single_score() {
+        let mut local = default_payload();
+        local.stats.best_single_score = 8_000; // local is better
+
+        let mut remote = default_payload();
+        remote.stats.best_single_score = 3_500;
+
+        let (merged, _) = merge(&local, &remote);
+        assert_eq!(
+            merged.stats.best_single_score, 8_000,
+            "merge must keep the higher best_single_score (local in this case)"
+        );
+    }
+
+    // -----------------------------------------------------------------------
+    // 3. Merge never removes an achievement that is unlocked on one side.
+    // -----------------------------------------------------------------------
+
+    #[test]
+    fn sync_merge_never_removes_unlocked_achievement() {
+        let mut unlocked = AchievementRecord::locked("first_win");
+        unlocked.unlock(Utc::now());
+
+        // local has the achievement unlocked; remote has no achievements at all.
+        let local = make_payload(StatsSnapshot::default(), vec![unlocked]);
+        let remote = make_payload(StatsSnapshot::default(), vec![]);
+
+        let (merged, _) = merge(&local, &remote);
+
+        let found = merged
+            .achievements
+            .iter()
+            .find(|a| a.id == "first_win")
+            .expect("achievement must survive the merge");
+        assert!(
+            found.unlocked,
+            "achievement unlocked on local must remain unlocked after merge with remote that lacks it"
+        );
+    }
+
+    // -----------------------------------------------------------------------
+    // 4. merge(payload, payload) is idempotent for key numeric fields.
+    // -----------------------------------------------------------------------
+
+    #[test]
+    fn sync_merge_is_idempotent() {
+        let mut payload = default_payload();
+        payload.stats.games_played = 42;
+        payload.stats.games_won = 20;
+        payload.stats.best_single_score = 5_500;
+        payload.stats.fastest_win_seconds = 90;
+        payload.stats.lifetime_score = 110_000;
+        payload.progress.total_xp = 3_000;
+
+        let (merged, _) = merge(&payload, &payload);
+
+        assert_eq!(merged.stats.games_played, 42, "idempotent: games_played");
+        assert_eq!(merged.stats.games_won, 20, "idempotent: games_won");
+        assert_eq!(merged.stats.best_single_score, 5_500, "idempotent: best_single_score");
+        assert_eq!(merged.stats.fastest_win_seconds, 90, "idempotent: fastest_win_seconds");
+        assert_eq!(merged.stats.lifetime_score, 110_000, "idempotent: lifetime_score");
+        assert_eq!(merged.progress.total_xp, 3_000, "idempotent: total_xp");
+    }
+}