Hygiene B3: single-sourcing & magic-number consolidation

- StructureCatalogAuthoring: WallCostOre -> WallCostBiomass (it bakes a Biomass cost; [FormerlySerializedAs] preserves the scene value).
- Harvester/Fabricator authoring: resource-id byte defaults reference ResourceId.Ore/.Charge instead of magic 2/4.
- RegionMath.RegionBoundaryX (= ExpeditionOffsetX*0.5) single-sources the region-flip X used by HudSystem + OnboardingSystem (was 500f in 3 places).
- CharacterComponent.DefaultGroundedSharpness single-sources the CC sharpness 15f (GetDefault, DashSystem, PlayerDeathStateSystem, PlayerCharacterAuthoring).
- InventorySlot [InternalBufferCapacity] references Tuning.InventoryMaxSlots.
- ConnectionMode enum -> byte-const class (project convention; removes the latent enum-in-Burst trap); field + one Seed() param become byte.
- Tuning.ChargerWindupTicks single-sources the Charger telegraph windup (EnemyBaker + TuningConfig.Defaults; was a bare 30 that could drift).
- (TicksPerSecond deliberately NOT added: no seconds->ticks conversion site exists; the tick-count fields are per-authoring designer tunables, so a const would be unreferenced.)

451/451 EditMode tests pass.

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

Assets/_Project/Scripts/Simulation/World/RegionComponents.cs

@@ -42,6 +42,10 @@ namespace ProjectM.Simulation
         /// transiently-coexisting arenas can never interact in the shared PhysicsWorld.</summary>
         public const float RoomStrideX = 500f;
 
+        /// <summary>Region-flip boundary X (half the expedition offset): a player/camera past this reads as the
+        /// +1000 expedition region. Single source for the HUD / onboarding / atmosphere region checks (DR-013).</summary>
+        public const float RegionBoundaryX = ExpeditionOffsetX * 0.5f;
+
         /// <summary>
         /// World-space origin of expedition room sub-slot <paramref name="subSlot"/> (0 or 1 — the run FSM
         /// ping-pongs consecutive rooms between two offsets so the next room spawns at the idle slot while the