feat(frontend)!: sveltekit 3 on the v0.7.0 template, typescript 6, adapter-auto dropped; backend base moves to trixie

frontend/src/env.ts

@@ -0,0 +1,5 @@
+import { defineEnvVars } from "@sveltejs/kit/env";
+
+export const variables = defineEnvVars({
+  PUBLIC_API_BASE_URL: { public: true, schema: (input) => input ?? "/api" },
+});