feat(mvp): phase 8 - integration, testing & deployment

Fix all build/type/lint errors (zod 3.25 compat wrapper, Svelte 5 fixes),
write 115 unit tests across 10 test files, expand seed script with demo
data, update Docker config with migration on startup.

vite.config.ts

@@ -6,7 +6,7 @@ export default defineConfig({
 	plugins: [tailwindcss(), sveltekit()],
 	test: {
 		include: ['src/**/*.{test,spec}.{js,ts}'],
-		environment: 'jsdom',
+		environment: 'node',
 		globals: true,
 		setupFiles: []
 	}