fix(client): address PR #78 review comments

- Widen world_seed entropy from u32 to full u64 by combining two randi()
  calls (Hoshe warning #1)
- Persist world_seed to save directory and restore on resume_game() so
  loaded sessions maintain D-010 deterministic replay (Tyre warning #2)
- Constrain EntanglementConfig intrigue range based on flat value so
  mundane_ratio stays within D-029 spec [45,55]% (both reviewers)
- Remove dead VIS_PERIPHERAL constant and _grow_bounds() method
- Update test_client_p1 peripheral test for forward-only simplification
- Fix misleading exp_fade shader comment (filter_nearest = hard step)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/shaders/fog.gdshader

@@ -90,8 +90,9 @@ void fragment() {
     float alpha = mix(fog_alpha, 0.0, clarity);
     vec3 color = mix(FOG_OVERLAY_COLOR, vec3(0.0), clarity);
 
-    // Soft transition at the explored/unexplored tile boundary.
+    // Hard step at the explored/unexplored tile boundary.
     // exploration_tex uses filter_nearest: explored is exactly 0.0, ~0.5, or 1.0.
+    // smoothstep maps these to 0.0 or 1.0 — no sub-tile blending.
     float exp_fade = smoothstep(0.0, 0.2, explored);
     alpha = mix(1.0, alpha, exp_fade);
     color = mix(UNEXPLORED_COLOR, color, exp_fade);