fix(simulation): address PR #55 review — stale comment, range, duplication, docs

- Fix protocol version comment (12 → 13) in ObserverSnapshot doc
- Widen Want intensity range from 3..=9 to 1..=10 to match spec and test
- Replace duplicated pool selection in trigger_recognition_monologue with
  call to select_pool_line helper (~50 lines removed)
- Document NaiveSpatialIndex migration cost for grid/quadtree swap
- Remove misleading Default derive from TellCategory (Nervous is not a
  sensible default for neutral NPCs)
- Add caller invariant doc on generate_npc (no TilePosition spawned)

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

server/src/simulation/spatial.rs

@@ -33,6 +33,16 @@ pub trait SpatialIndex: Send + Sync {
 /// Replace with grid or quadtree when profiling shows this is a bottleneck.
 /// Deterministic iteration: entries stored in insertion order, but callers
 /// should not depend on ordering (sort by Entity::to_bits() if needed).
+///
+/// ## Migration cost for grid/quadtree swap
+///
+/// `sync_spatial_index` takes `ResMut<NaiveSpatialIndex>` directly because
+/// bevy_ecs cannot store `dyn SpatialIndex` as a Resource. A swap to Grid or
+/// BVH requires changing the concrete type in: (1) `sync_spatial_index` system
+/// parameter, (2) `SimulationPlugin` resource registration, (3) any system
+/// that queries `Res<NaiveSpatialIndex>` (currently: `update_follow_state`).
+/// The `SpatialIndex` trait ensures the API surface stays identical — only the
+/// type name changes at call sites. Estimated: ~5 lines per caller.
 #[derive(Resource, Debug, Default)]
 pub struct NaiveSpatialIndex {
     entries: Vec<(Entity, TilePosition)>,