Hygiene B2: dead-code removal

Delete (unreferenced in any scene, per operator decision):
- TrainingDummy* chain (authoring/spawner/system/components/prefab) + UpgradePickup* chain (authoring/spawner/systems/components/prefab); remove TrainingDummyTag from the 3 live combat queries (AbilityFire/Melee/HealthApplyDamage now key on EnemyTag) and repoint HealthApplyDamageSystemTests to EnemyTag.
- Dead RPC RegionTransitSystem + RegionTransitRequest (no sender, ungated) + its test.
- Heartbeat + HeartbeatSystem (no WorldSystemFilter, ran no-op every tick) + its test.
- BuildSendSystem dead conveyor/pylon dev hooks (s_ConveyorDir, [/] rotation, Place{Pylon,Harvester,Conveyor} statics).
- Deprecated CyclePhase alias consts (Expedition/Defend/Build/*Ticks); repoint WaveSystemTests to Siege/Calm.
- Unread FeelConfig fields (HitFlashDurationMs, RumbleHeavy) + dangling HudUi doc-comments + stale crefs.

451/451 EditMode tests pass. CLAUDE.md HeartbeatSystemTests example ref to be repointed in B7.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Assets/_Project/Scripts/Simulation/Combat/Health.cs

@@ -7,7 +7,7 @@ namespace ProjectM.Simulation
     /// Hit points for any damageable ghost (players, training dummies). Server-authoritative:
     /// only server systems write <see cref="Current"/>; clients receive it via the [GhostField]
     /// for display and prediction reconciliation. <see cref="Max"/> is baked identically on both
-    /// worlds and is not replicated. Added by PlayerBaker / TrainingDummyBaker.
+    /// worlds and is not replicated. Added by PlayerBaker.
     /// </summary>
     public struct Health : IComponentData
     {