Phase 1: Core hex engine, Leaflet overlay, terrain painting UI

- core/: Pure TS hex engine (axial coords, hex grid, terrain types,
  edge connectivity with constraint solver, HexMap state model)
- src/map/: Leaflet L.CRS.Simple map init, Canvas-based hex overlay
  layer (L.GridLayer), click/edge interaction detection
- src/ui/: Sidebar with toolbar (Select/Paint/Feature modes),
  terrain picker, hex inspector, map settings (hex size, grid, opacity)
- pipeline/: Tile pyramid generator (sharp, from source image)
- tests/: 32 passing tests for coords, hex-grid, edge-connectivity
- Uses Kiepenkerl tiles (symlinked) for development

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/terrain.ts

@@ -0,0 +1,36 @@
+import type { TerrainType } from './types.js';
+
+export const TERRAIN_TYPES: TerrainType[] = [
+  // Area fills (drawn first, below linear features)
+  { id: 'ocean',      name: 'Ocean/Sea',   category: 'area',   color: '#2a5574', zIndex: 0 },
+  { id: 'lake',       name: 'Lake',        category: 'area',   color: '#4a90c4', zIndex: 1 },
+  { id: 'plains',     name: 'Plains',      category: 'area',   color: '#c4b060', zIndex: 2 },
+  { id: 'farmland',   name: 'Farmland',    category: 'area',   color: '#a4c639', zIndex: 3 },
+  { id: 'forest',     name: 'Forest',      category: 'area',   color: '#2d6a2d', zIndex: 4 },
+  { id: 'hills',      name: 'Hills',       category: 'area',   color: '#8a7a5a', zIndex: 5 },
+  { id: 'mountains',  name: 'Mountains',   category: 'area',   color: '#6a6a6a', zIndex: 6 },
+  { id: 'settlement', name: 'Settlement',  category: 'area',   color: '#8b4513', zIndex: 7 },
+  // Linear features (drawn on top, have edge connectivity)
+  { id: 'river',      name: 'River',       category: 'linear', color: '#2a7fff', zIndex: 10 },
+  { id: 'road',       name: 'Road',        category: 'linear', color: '#a0522d', zIndex: 11 },
+  { id: 'coastline',  name: 'Coastline',   category: 'linear', color: '#1a4a6a', zIndex: 12 },
+];
+
+const terrainMap = new Map<string, TerrainType>(
+  TERRAIN_TYPES.map(t => [t.id, t]),
+);
+
+export function getTerrainType(id: string): TerrainType | undefined {
+  return terrainMap.get(id);
+}
+
+export function getAreaTerrains(): TerrainType[] {
+  return TERRAIN_TYPES.filter(t => t.category === 'area');
+}
+
+export function getLinearTerrains(): TerrainType[] {
+  return TERRAIN_TYPES.filter(t => t.category === 'linear');
+}
+
+/** Default terrain for unpainted hexes */
+export const DEFAULT_BASE_TERRAIN = 'plains';