fix(simulation): address all round 3 PR review issues

- Register StorytellerPlugin in main() and dump_schedule_graph() so
  contamination system runs in production (critical, rounds 2+3)
- Add doc comment to z_bands_connected clarifying band indices vs
  absolute z-levels (D-110)
- Add TODO on hardcoded modifications: vec![] in save_to_file
- Init ContaminationActive in minimal_world() test helper
- Replace ChaCha20Rng with SimRng in fuzzy_map tests (D-010)

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

server/tests/fuzzy_map.rs

@@ -12,9 +12,8 @@
 //! Spec reference: D-010 (deterministic simulation, SimRng seeding), D-030 (testability)
 
 use rand::Rng;
-use rand::SeedableRng;
-use rand_chacha::ChaCha20Rng;
 use settled_reach_server::simulation::movement::{TilePosition, WalkabilityMap};
+use settled_reach_server::simulation::rng::SimRng;
 use std::collections::VecDeque;
 
 // ── Map generation constants ────────────────────────────────────────────────
@@ -63,7 +62,7 @@ struct ProceduralMap {
 // ── Map generator ─────────────────────────────────────────────────────────────
 
 fn generate_map(seed: u64) -> ProceduralMap {
-    let mut rng = ChaCha20Rng::seed_from_u64(seed);
+    let mut rng = SimRng::new(seed).rng;
     let mut wm = WalkabilityMap::new_blocked(MAP_W, MAP_H, 1);
     let mut rooms: Vec<Room> = Vec::new();
     let mut door_placements: Vec<DoorPlacement> = Vec::new();