feat(simulation): integer-deterministic Layer-3 settlement placement (#955)

Wire the existing attractor-matching engine (#919/#925) into the
generation cascade as Layer 3, and make the whole placement-scoring path
integer-deterministic.

Layer 3 (D-211):
- CascadeLayer::Settlement + Layer3Output (placements) on the snapshot;
  BodyWorldState gains a `placements` field (the D-203 hot cache).
- run_layer3 runs the five-phase match_cities against Layer-1 attractors
  via the authored D-195 compatibility matrix; pure function of
  (attractors, cities) — no RNG. cities are passed in by the caller so the
  cascade stays DB-free and testable. A `// cache seam` marks where a
  persistent cache wraps it later (#1021).
- gen_queue passes &[] for now (Topography needs no cities); the runtime
  settlement read (gen_queue/layer_proxy) is the #955 follow-on.

Integer determinism (D-010 / D-227 — D-195 amended):
- Wiring match_cities into the deterministic cascade made its f32 scoring
  a live cross-platform divergence risk (a near-tie comparison or the
  Hungarian's f32 reductions can round differently per platform → a
  different world from the same seed). Converted the entire path to
  integers: CompatibilityMatrix is a 0-100 affinity table; attractor
  strength is 0-100 and terrain cost is a percent (100 = baseline),
  quantized once at the Layer-1 feature boundary; cell_score, the
  Hungarian, and CityPlacement.score are i64. No f32 in any placement or
  ranking decision.
- Layer-1 golden fixture rebaked: confirmed selection/positions are
  unchanged (same 256 attractors, 93 river cells) — only the strength/cost
  representation changed.

Tests: lib green (1292); new settlement_layer_places_cities_deterministically
covers placement + determinism + propagation into BodyWorldState.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/src/simulation/generator.rs

@@ -439,27 +439,62 @@ pub struct GeographicAttractor {
     /// Pixel position in heightmap space [row, col].
     pub position: (u16, u16),
     pub attractor_type: AttractorType,
-    /// Normalized strength 0.0–1.0. Derived from flow accumulation or habitability score.
-    pub strength: f32,
+    /// Strength on a 0–100 integer scale (100 = strongest). Quantized from flow
+    /// accumulation / habitability at Layer-1 output. Integer for D-010
+    /// determinism — every ranking/scoring decision is exact, no f32 (#955).
+    pub strength: i32,
     /// Fine-grained terrain classification at this position (D-210).
     pub sub_biome: SubBiomeVariant,
-    /// Infrastructure-build cost multiplier (1.0 = baseline grassland; higher =
-    /// more expensive). Derived from `sub_biome` + local slope. Consumed by the
-    /// attractor-matching pipeline (D-211) to penalize marginal cities. (D-210)
-    pub terrain_modification_cost: f32,
+    /// Infrastructure-build cost as a percent of baseline (100 = baseline
+    /// grassland; >100 = more expensive, e.g. 200 = 2× cost). Derived from
+    /// `sub_biome` + local slope; penalizes marginal cities in the matching
+    /// pipeline (D-211). Integer for D-010 determinism (#955). (D-210)
+    pub terrain_modification_cost: i32,
 }
 
 /// Compatibility weights between economic roles and attractor types.
 /// A 10×7 matrix (10 economic_role values × 7 AttractorType variants).
-/// Each cell is a weight multiplier 0.0–3.0 applied during attractor-matching scoring.
-/// Source: D-195
+/// Each cell is an integer affinity 0–100 (100 = ideal terrain for that role,
+/// ~50 = neutral, low = poor) used during attractor-matching scoring.
+/// Integer for D-010 determinism (#955). Source: D-195
 #[derive(Serialize, Deserialize, Clone, Debug)]
 pub struct CompatibilityMatrix {
     /// Row order: manufacturing, financial, agricultural, extraction, service_mixed,
     ///   institutional, transit_hub, research, military, residential.
     /// Column order: RiverMouth, CoastalAccess, RiverCrossing, ValleyFloor,
     ///   PassEntrance, LakeShore, PlainCenter.
-    pub weights: [[f32; 7]; 10],
+    pub weights: [[i32; 7]; 10],
+}
+
+impl CompatibilityMatrix {
+    /// The canonical D-195 authored compatibility table (#955).
+    ///
+    /// Integer affinity 0–100: 100 = ideal terrain for the role, ~50 = neutral,
+    /// low (10–30) = poor fit (graduated, never a hard 0 — D-195). Re-authored
+    /// on the 0–100 scale from D-195's relative examples (the agricultural→
+    /// ValleyFloor 3.0 peak maps to the global max 100).
+    ///
+    /// Rows: manufacturing, financial, agricultural, extraction, service_mixed,
+    ///       institutional, transit_hub, research, military, residential.
+    /// Cols: RiverMouth, CoastalAccess, RiverCrossing, ValleyFloor,
+    ///       PassEntrance, LakeShore, PlainCenter.
+    pub fn d195() -> Self {
+        CompatibilityMatrix {
+            weights: [
+                // RMth Coast RXing Vall Pass Lake Plain
+                [95, 80, 75, 60, 30, 35, 55],  // manufacturing
+                [70, 90, 65, 25, 40, 45, 70],  // financial
+                [85, 30, 55, 100, 10, 70, 90], // agricultural
+                [30, 35, 40, 65, 95, 30, 25],  // extraction
+                [60, 65, 70, 50, 35, 50, 70],  // service_mixed
+                [65, 65, 60, 45, 20, 55, 90],  // institutional
+                [65, 75, 100, 35, 95, 25, 60], // transit_hub
+                [40, 70, 35, 75, 40, 95, 60],  // research
+                [60, 75, 80, 55, 100, 25, 40], // military
+                [70, 85, 50, 65, 20, 85, 70],  // residential
+            ],
+        }
+    }
 }
 
 // ---------------------------------------------------------------------------