feat(citygen): tile, world and net data model

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

crates/citygen/src/params.rs

@@ -0,0 +1,76 @@
+//! Generation parameters.
+
+use crate::geom::Size;
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone, Copy, Debug, PartialEq, Serialize, Deserialize)]
+pub enum SizePreset {
+    Small,
+    Medium,
+    Large,
+    Custom { w: u32, h: u32 },
+}
+
+impl SizePreset {
+    pub fn size(self) -> Size {
+        match self {
+            SizePreset::Small => Size { w: 160, h: 80 },
+            SizePreset::Medium => Size { w: 240, h: 120 },
+            SizePreset::Large => Size { w: 320, h: 160 },
+            SizePreset::Custom { w, h } => Size { w, h },
+        }
+    }
+
+    pub fn label(self) -> &'static str {
+        match self {
+            SizePreset::Small => "small",
+            SizePreset::Medium => "medium",
+            SizePreset::Large => "large",
+            SizePreset::Custom { .. } => "custom",
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub enum WaterMode {
+    None,
+    Bay,
+    River,
+}
+
+impl WaterMode {
+    pub fn label(self) -> &'static str {
+        match self {
+            WaterMode::None => "none",
+            WaterMode::Bay => "bay",
+            WaterMode::River => "river",
+        }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct GenParams {
+    pub seed: u64,
+    pub size: SizePreset,
+    pub districts: u8,
+    pub density: f32,
+    pub wealth_skew: f32,
+    pub decay: f32,
+    pub water: WaterMode,
+    pub flavor: String,
+}
+
+impl Default for GenParams {
+    fn default() -> Self {
+        GenParams {
+            seed: 0,
+            size: SizePreset::Medium,
+            districts: 7,
+            density: 0.6,
+            wealth_skew: 0.0,
+            decay: 0.4,
+            water: WaterMode::Bay,
+            flavor: "default".into(),
+        }
+    }
+}