Add CLAUDE.md, switch to static adapter for nginx deployment

- CLAUDE.md: build commands, architecture overview, coordinate systems,
  WASM rebuild instructions for future development sessions
- Switch from adapter-auto to adapter-static with SPA fallback
  (outputs to build/ directory for nginx serving)
- Install @sveltejs/adapter-static dependency

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

frontend/svelte.config.js

@@ -1,16 +1,14 @@
-import adapter from '@sveltejs/adapter-auto';
+import adapter from '@sveltejs/adapter-static';
 
 /** @type {import('@sveltejs/kit').Config} */
 const config = {
 	compilerOptions: {
-		// Force runes mode for the project, except for libraries. Can be removed in svelte 6.
 		runes: ({ filename }) => (filename.split(/[/\\]/).includes('node_modules') ? undefined : true)
 	},
 	kit: {
-		// adapter-auto only supports some environments, see https://svelte.dev/docs/kit/adapter-auto for a list.
-		// If your environment is not supported, or you settled on a specific environment, switch out the adapter.
-		// See https://svelte.dev/docs/kit/adapters for more information about adapters.
-		adapter: adapter()
+		adapter: adapter({
+			fallback: 'index.html',
+		}),
 	}
 };