add nix development environment

Provide a direnv-loaded Laravel and future Vue toolchain with isolated worktree ports and a process-compose stack. Use PostgreSQL for local runtime services while retaining in-memory SQLite for PHPUnit.

Caddyfile

@@ -0,0 +1,17 @@
+{
+	auto_https off
+	admin off
+}
+
+localhost:{$CADDY_PORT:8000}, 127.0.0.1:{$CADDY_PORT:8000} {
+	tls .cert/localhost.pem .cert/localhost-key.pem
+
+	handle /storage/* {
+		root * backend/public
+		file_server
+	}
+
+	handle {
+		reverse_proxy 127.0.0.1:{$BACKEND_PORT:8001}
+	}
+}