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/src/simulation/generator.rs

@@ -345,7 +345,8 @@ pub struct FloorZone {
 pub struct VerticalCorridorSpec {
     /// Which blocks this vertical corridor passes through.
     pub block_coords: Vec<(u8, u8)>,
-    /// Which z-bands this corridor connects.
+    /// Which z-bands (0-indexed band indices, not absolute z-levels) this
+    /// corridor connects. See D-110 for signed z-level coordinate system.
     pub z_bands_connected: Vec<u8>,
     pub access_tier: AccessTier,
     pub corridor_type: VerticalCorridorType,