feat(progression): read surface and change announcements (slice 10a)

reads for the UI: TotalCoins, Lives, IsRunOver, CurrentLevel,
LevelOf/IsOwned/CanAfford, HasCleared. The read half of candidate 01 -
callers get a narrow surface instead of reaching into state.

new domain events LivesChanged / TotalCoinsChanged / SkillSetChanged,
announced by comparing against the last announced value, so an operation
can neither forget to announce nor announce something unchanged.

HandlePlayerDeath now clears the spent attempt - it was still counting
towards TotalCoins after its ledger had been discarded.

republisher and EventBus extended; SkillSetChanged is what SkillManager
will reconcile against instead of the non-atomic call pairs. 65 tests.

progression/ProgressionEvent.cs

@@ -22,3 +22,21 @@ public sealed record AchievementUnlocked(AchievementId Achievement) : Progressio
 /// this, so an entry path that does not announce is an entry path where neither works.
 /// </summary>
 public sealed record LevelStarted(LevelId Level) : ProgressionEvent;
+
+/// <summary>
+/// Lives remaining changed. Raised by the same operation that changed them, so no reader can observe
+/// a stale value between the write and the announcement.
+/// </summary>
+public sealed record LivesChanged(Lives Remaining) : ProgressionEvent;
+
+/// <summary>
+/// Spendable coins changed — the Bank plus the current Attempt's takings, less what it has spent.
+/// A single fact for readers, so nothing has to know the Attempt and Bank are separate.
+/// </summary>
+public sealed record TotalCoinsChanged(Coins Total) : ProgressionEvent;
+
+/// <summary>
+/// The set of owned Skills, or the level of one of them, changed. What <c>SkillManager</c> reconciles
+/// its live components against, instead of being told separately by every caller.
+/// </summary>
+public sealed record SkillSetChanged : ProgressionEvent;