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/leaderboard.rs

@@ -152,3 +152,71 @@ pub async fn opt_in(
 
     Ok(Json(serde_json::json!({ "ok": true })))
 }
+
+// ---------------------------------------------------------------------------
+// Tests — data shape and display-name logic; no database required
+// ---------------------------------------------------------------------------
+
+#[cfg(test)]
+mod tests {
+    use chrono::Utc;
+    use solitaire_sync::LeaderboardEntry;
+
+    /// Helper that constructs a `LeaderboardEntry` with the given display name
+    /// and best score. `best_time_secs` is left as `None`.
+    fn entry(display_name: &str, best_score: Option<i32>) -> LeaderboardEntry {
+        LeaderboardEntry {
+            display_name: display_name.to_string(),
+            best_score,
+            best_time_secs: None,
+            recorded_at: Utc::now(),
+        }
+    }
+
+    // -----------------------------------------------------------------------
+    // 1. A LeaderboardEntry always carries a non-empty display_name.
+    // -----------------------------------------------------------------------
+
+    #[test]
+    fn leaderboard_entry_has_display_name() {
+        let e = entry("Alice", Some(4_500));
+        assert!(
+            !e.display_name.is_empty(),
+            "display_name must not be empty for a valid leaderboard entry"
+        );
+        assert_eq!(e.display_name, "Alice");
+    }
+
+    // -----------------------------------------------------------------------
+    // 2. A Vec of entries sorts by best_score descending (matching the SQL
+    //    ORDER BY used in get_leaderboard).
+    // -----------------------------------------------------------------------
+
+    #[test]
+    fn leaderboard_entries_sorted_by_score_descending() {
+        let mut entries = vec![
+            entry("Charlie", Some(1_200)),
+            entry("Alice",   Some(8_000)),
+            entry("Bob",     Some(3_500)),
+            entry("Dave",    None),        // no score — should rank last
+        ];
+
+        // Mirrors the SQL sort:
+        //   CASE WHEN best_score IS NULL THEN 1 ELSE 0 END ASC,
+        //   best_score DESC
+        entries.sort_by(|a, b| {
+            let a_null = a.best_score.is_none() as u8;
+            let b_null = b.best_score.is_none() as u8;
+            a_null
+                .cmp(&b_null)
+                .then_with(|| b.best_score.cmp(&a.best_score))
+        });
+
+        // Scored entries first, in descending order.
+        assert_eq!(entries[0].display_name, "Alice",   "highest scorer must be first");
+        assert_eq!(entries[1].display_name, "Bob",     "second-highest scorer must be second");
+        assert_eq!(entries[2].display_name, "Charlie", "lowest scorer must be third");
+        // Null-score entry sinks to the bottom.
+        assert_eq!(entries[3].display_name, "Dave",    "entry with no score must rank last");
+    }
+}