style(server): clear clippy-1.93 cfg(test)/test-target debt (#967)

Manual clippy-1.93 fixes that the prior machine-applicable sweep couldn't auto-
apply, all in cfg(test) modules and tests/ targets (invisible to the lib-only
pre-push clippy, hence accumulated unflagged):

- disallowed_types HashSet/HashMap → BTreeSet/BTreeMap (determinism rule):
  shadowcast_bench.rs (×8, (i32,i32) keys), mood.rs, sound.rs. SoundEventKind
  gains a PartialOrd/Ord derive (fieldless Copy enum) so it is BTree-usable.
- field_reassign_with_default → struct-init: disclosure.rs, monologue.rs (×2),
  save_io.rs (keeps `mut` for the deliberate last-write-wins overwrite).
- assertions_on_constants on the EAVESDROP_THRESHOLD invariant → compile-time
  `const _: () = assert!(...)`: listening.rs, cross_room_transitions.rs. This is
  stronger than the runtime assert and needs no #[allow].
- approx_constant: settings/types.rs round-trip literal 3.14 → 2.5 (the value is
  arbitrary test data, never meant to be PI — change avoids both the lint and a
  suppression).
- drop_non_drop: vision.rs early Mut<WalkabilityMap> release → scoped block.
- unnecessary_get_then_check → contains_key: information_boundaries.rs (×3).
- cloned_ref_to_slice_refs → std::slice::from_ref: triangle_validation.rs.
- unused_must_use: input.rs dropped the unused .id() on a spawn.

cargo clippy --all-targets -- -D warnings is clean; cargo test green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/src/simulation/input.rs

@@ -2601,9 +2601,7 @@ mod tests {
         });
         world.insert_resource(registry);
 
-        world
-            .spawn((PlayerCharacter, TilePosition::new(5, 5, 0)))
-            .id();
+        world.spawn((PlayerCharacter, TilePosition::new(5, 5, 0)));
         world
     }
 

server/src/simulation/listening.rs

@@ -441,13 +441,9 @@ mod tests {
     fn eavesdrop_threshold_careful_less_than_normal() {
         // T4: The careful threshold MUST be strictly less than the normal
         // threshold — careful stance rewards patience with faster eavesdrop
-        // activation (D-053, D-018).
-        assert!(
-            EAVESDROP_THRESHOLD_CAREFUL < EAVESDROP_THRESHOLD,
-            "EAVESDROP_THRESHOLD_CAREFUL ({}) must be < EAVESDROP_THRESHOLD ({})",
-            EAVESDROP_THRESHOLD_CAREFUL,
-            EAVESDROP_THRESHOLD,
-        );
+        // activation (D-053, D-018). Compile-time invariant: pins the ordering
+        // so a future const edit can't silently invert it.
+        const _: () = assert!(EAVESDROP_THRESHOLD_CAREFUL < EAVESDROP_THRESHOLD);
     }
 
     // -----------------------------------------------------------------------

server/src/simulation/monologue.rs

@@ -819,12 +819,13 @@ mod tests {
         queue.push_anomaly(42, 0);
 
         // Pre-fill the monologue buffer (as if trigger_monologue already wrote)
-        let mut buffer = MonologueBuffer::default();
-        buffer.event = Some(MonologueEvent {
-            id: "existing_line".to_string(),
-            text: "I should keep this.".to_string(),
-            duration_seconds: 5.0,
-        });
+        let buffer = MonologueBuffer {
+            event: Some(MonologueEvent {
+                id: "existing_line".to_string(),
+                text: "I should keep this.".to_string(),
+                duration_seconds: 5.0,
+            }),
+        };
 
         world.spawn((
             PlayerCharacter,
@@ -1074,12 +1075,13 @@ mod tests {
         });
 
         // Pre-fill MonologueBuffer (e.g., from trigger_monologue)
-        let mut buffer = MonologueBuffer::default();
-        buffer.event = Some(MonologueEvent {
-            id: "existing_line".to_string(),
-            text: "Already have something to say.".to_string(),
-            duration_seconds: 5.0,
-        });
+        let buffer = MonologueBuffer {
+            event: Some(MonologueEvent {
+                id: "existing_line".to_string(),
+                text: "Already have something to say.".to_string(),
+                duration_seconds: 5.0,
+            }),
+        };
 
         world.spawn((
             PlayerCharacter,

server/src/simulation/save_io.rs

@@ -756,11 +756,11 @@ mod tests {
     /// The warn! in process_player_input fires; here we just confirm last-write-wins.
     #[test]
     fn pending_command_overwrite_last_write_wins() {
-        let mut pending = SaveLoadPending::default();
-
-        pending.pending = Some(SaveLoadCommand::Save {
-            path: PathBuf::from("/tmp/first.msgpack"),
-        });
+        let mut pending = SaveLoadPending {
+            pending: Some(SaveLoadCommand::Save {
+                path: PathBuf::from("/tmp/first.msgpack"),
+            }),
+        };
         // Overwrite with a Load command
         pending.pending = Some(SaveLoadCommand::Load {
             path: PathBuf::from("/tmp/second.msgpack"),

server/src/simulation/sound.rs

@@ -17,7 +17,7 @@ use crate::simulation::movement::TilePosition;
 
 /// Typed sound event categories.
 /// Client maps each kind to its audio asset registry key (D-038).
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
 pub enum SoundEventKind {
     /// Footstep — emitted by moving entities. Intensity varies by stance.
     Footstep,
@@ -464,7 +464,7 @@ mod tests {
             "all five SoundEventKind variants collected"
         );
 
-        let collected_kinds: std::collections::HashSet<SoundEventKind> =
+        let collected_kinds: std::collections::BTreeSet<SoundEventKind> =
             queue.events.iter().map(|e| e.kind).collect();
         for kind in [
             SoundEventKind::Footstep,