Hazard: Blight geyser — permanent periodic both-sides AoE (Phase 1.5b bundle 3)

Review-first netcode slice (design review wf_900e9965-8f0 -> 11 folded;
post-impl wf_5c8299f8-299 clean). A PERMANENT periodic telegraphed AoE in
Blight-biome rooms only; one new [GhostField] uint NextEruptTick.

- Geyser component + GeyserEruptSystem (server): inverted invalid-tick guard
  (a baked-0 tick must NEVER erupt -> lazy-stamps born-correct instead of the
  party-wiping per-tick barrage), inline both-sides gather (SourceNetworkId=-1),
  reschedule = now + period (never +=), never destroyed.
- GeyserTelegraphSystem (client): absolute-tick growing warning disc +
  erupt burst on the >0->=<0 crossing, latched per NextEruptTick + arm-guard
  (never edge-detects the replicated field -> no phantom on 0->stamp /
  relevancy re-entry). Reuses ScorchDecalSystem + DynamicLightSystem.
- Seeded in RoomFieldSystem (Blight-gated on plan.Biome, born-correct staggered
  stamp from live ServerTick), GeyserFieldSpawner + authoring wired into the
  Gameplay subscene. Geyser.prefab duplicated from ResourceNode (no collider).
- BuildDisc promoted to FeedbackFx (shared with the barrel fuse ring).
- 474/474 EditMode incl. the unstamped-storm regression; live no-storm end-to-end.

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

Assets/_Project/Subscenes/Gameplay.unity

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