Scale difficulty by run position; wipe towers at phase end

Follow-up pass on the 2.0 refactor, closing the gap between "waves are drawn
at random" and "difficulty still lives in the enemy assets".

- Enemy health is no longer authored per enemy type. New EnemyScalingConfig
  scales a per-zone HP *budget* by encounter number; per-enemy health is that
  budget divided by the wave's enemy count. Scaling the total rather than the
  per-enemy value keeps enemy count a texture knob (few tanks vs many swarmers)
  instead of a second, uncontrolled difficulty axis. EnemyDefinition.MaxHp
  becomes HpMultiplier, a deviation around 1.0. Speed stays archetype-only and
  unscaled -- escalating it compounds with health and invalidates tower balance
  mid-run.
- GoldConfig entries no longer reference a WaveDefinition. Payout is a property
  of run position, not of which wave got drawn: WaveGoldEntry ->
  EncounterGoldEntry, Waves -> Encounters, keyed by global encounter number.
  Its inspector labels elements "Encounter N" and projects cumulative earnings.
- The wave's voted buffs now show as icon badges in the top bar, read from the
  same RunState slot the spawn path uses so the display can't drift from what
  the enemies actually carry. Hover names the buff; unillustrated cards fall
  back to a lettered badge rather than vanishing.
- Clearing a phase's boss destroys every built tower, unrefunded. Queued build
  jobs still refund -- those towers were never delivered. Runs with the field
  empty, so the walkability churn doesn't hit the re-path scheduler.
- Fixed an RPC codegen break: [ClientRpc] requires a ClientRpc suffix, unlike
  the newer [Rpc(SendTo...)] style this file doesn't use.
- Setup checklist reordered into dependency order; it previously asked for a
  RunDefinition two sections before creating one.

Also carries the editor-side asset reorganisation into Definitions/RunDefinitions
and the sprite move into Enemy/Player draft icon folders.

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

Assets/_Project/Scripts/Gameplay/Waves/WaveGroup.cs

@@ -19,7 +19,7 @@ namespace TD.Gameplay.Waves
     /// <para>A class rather than a struct specifically so <see cref="Weight"/> can carry a
     /// field initializer — Unity runs it when the inspector creates a fresh array element,
     /// which is what gives new entries their equal-by-default weighting. Mirrors
-    /// <see cref="WaveGoldEntry"/>.</para>
+    /// <see cref="EnemyUpgrades.EnemyUpgradePoolEntry"/>.</para>
     /// </remarks>
     [Serializable]
     public class WavePoolEntry