Feel: Phase 1.5 lighting/atmosphere pass — dark ambient + dynamic lights

Dark-ambient, dynamic-light-first look (RoR2/Death Scourges reference),
built filter-agnostic so the pixel style composes on top:

- New DynamicLightSystem (client-only, PresentationSystemGroup): pooled
  point lights follow projectile ghosts; pulsing portal light during
  RoomExplore (same ExpeditionPortalPos authority as the beacon); soft
  resource-node glow that fades with harvest-shrink; short impact
  FLASHES fed by CombatFeedbackSystem's burst funnel (EmitColored +
  SpawnVfx -> RequestFlash). Knobs in DynamicLightConfig (scene object,
  code defaults when absent).
- Atmosphere darkened: WorldAtmosphereConfig/System palettes moved to
  the dark set (base cool dusk, arid burnt dusk, per-room biome consts
  darkened); scene fog switched Linear -> ExponentialSquared (the
  system's per-region DENSITY writes were dead in Linear mode);
  trilight ambient lowered; directional 1.9 -> 1.05 slightly warm.
- 6 landmark mood lights (warpgate cyan, artefact violet x2, survey
  camp warm x2, cabin warm); URP additional-lights-per-object 4 -> 8
  (was starving the existing Aether lights).
- Art-look gate material: Assets/Screenshots/artlook_{base,room}_
  pixel{ON,OFF}.png over the lit scene.

Verified: lights live in Play (20 static at base incl. new landmarks;
pooled dynamics active in-room: node glows + impact flashes), fog/
ambient values confirmed live, 466/466 EditMode, console clean.

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

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