feat(engine): contextual one-time tips — stall hint, radial menu teach (Phase I)

Two situation-fired teaches, each shown exactly once and recorded in
Settings like shown_achievement_onboarding:

- Stall tip: 45s with no board change in an active, started game
  (clock frozen while paused / a modal is open) points at Hint with
  platform-correct copy (H on desktop, bottom-bar Hint on touch).
- Radial teach: a player 15 moves into a game who has never opened the
  radial menu learns the long-press / right-click gesture. Organic
  radial use marks the tip done silently — nobody is taught what they
  already know.

Tips ride the queued InfoToastEvent path, so they render in the unified
toast stack and never interrupt play. This completes Phase I.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

solitaire_data/src/settings.rs

@@ -265,6 +265,16 @@ pub struct Settings {
     /// `#[serde(default)]`.
     #[serde(default)]
     pub last_seen_whats_new: String,
+    /// `true` once the one-shot "Stuck? Try a hint" contextual tip has
+    /// fired (or been suppressed as unnecessary). Phase I teach: fired
+    /// by the situation, shown once, like `shown_achievement_onboarding`.
+    #[serde(default)]
+    pub shown_stall_hint_tip: bool,
+    /// `true` once the one-shot radial-menu contextual tip has fired —
+    /// or the player has already opened the radial menu on their own,
+    /// which marks the tip as unnecessary without showing it.
+    #[serde(default)]
+    pub shown_radial_menu_tip: bool,
     /// Custom public name displayed on the leaderboard. When `None`, the
     /// player's server `username` is used instead. Trimmed to 32 characters
     /// before submission. Older `settings.json` files written before this
@@ -434,6 +444,8 @@ impl Default for Settings {
             last_difficulty: None,
             last_mode: GameMode::Classic,
             last_seen_whats_new: String::new(),
+            shown_stall_hint_tip: false,
+            shown_radial_menu_tip: false,
             leaderboard_display_name: None,
             leaderboard_opted_in: false,
             take_from_foundation: true,