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/Tuning.cs

@@ -12,7 +12,6 @@ namespace ProjectM.Simulation
     /// <para>
     /// <b>Values that already live in a clear, public, semantically-named home (NOT duplicated here):</b>
     /// <list type="bullet">
-    /// <item><see cref="CyclePhase.ExpeditionTicks"/> / <see cref="CyclePhase.BuildTicks"/> — cycle phase durations.</item>
     /// <item><see cref="RegionMath.ExpeditionOffsetX"/> — base→expedition world-space offset.</item>
     /// <item>Per-ability/character stats — authored in ScriptableObjects, baked to the AbilityDatabase blob (M3).</item>
     /// </list>