feat: coins and skills move to the new domain (commit B of the swap)

atomic pair - purchasing couples them, so neither moves alone.

SkillData.Level is gone. It was an [Export] on a cached Resource: one
instance per process, so the level never persisted, leaked between save
slots, and made "unowned" indistinguishable from "level 1". Level now
comes from the Playthrough and is passed to ISkill.Initialize.

SkillManager reconciles from SkillSetChanged instead of being told by
each caller. The old shape was "record it, then tell SkillManager" as two
calls at four sites; AddSkill's early return when no player is registered
left the skill owned but inert. Reconciliation also tracks the level each
component was built at, so an upgrade rebuilds it rather than being
patched in from outside.

SkillUnlockerComponent collapses to one TryBuy - unlock and upgrade were
two methods each doing affordability, debit, level mutation and manager
notification in order.

The guard three components copy-pasted around Upgrades[Level - 1] - and
which BrickArmor omitted - now lives once in SkillComponentBase.

Hud reads coins from CoinsChanged instead of rebuilding translated
strings every frame. Lives still polls; it moves with the death path.

scripts/Events/CoinStateHandler.cs

@@ -1,12 +1,16 @@
 using Godot;
 using Mr.BrickAdventures.Autoloads;
+using Mr.BrickAdventures.Progression;
 
 namespace Mr.BrickAdventures.scripts.Events;
 
 /// <summary>
-/// Handles coin collection events and updates the GameStateStore.
-/// Replaces the manual coin logic in GameManager.
+/// Records collected coins against the current Attempt.
 /// </summary>
+/// <remarks>
+/// Coins are banked only by a First Clear, so dying loses what was found this attempt — including
+/// anything spent from it. See docs/adr/0002-attempt-is-a-ledger.md.
+/// </remarks>
 public partial class CoinStateHandler : Node
 {
     public override void _Ready()
@@ -17,13 +21,13 @@ public partial class CoinStateHandler : Node
     public override void _ExitTree()
     {
         if (EventBus.Instance != null)
-        {
             EventBus.Instance.CoinCollected -= OnCoinCollected;
-        }
     }
 
     private void OnCoinCollected(int amount, Vector2 position)
     {
-        GameStateStore.Instance?.AddSessionCoins(amount);
+        if (amount <= 0) return;
+
+        ProgressionRoot.Instance?.RecordCoinsFound(Coins.Of(amount));
     }
 }