feat(deploy): configurable backend HOST + env-driven vite base/assetsDir

- backend: HOST env (default 127.0.0.1, dev-safe; 0.0.0.0 in container)
- frontend: VITE_BASE drives base/assetsDir/manifest for portal embedding
- backward compatible: no env => identical to previous behavior

backend/test/config.test.ts

@@ -0,0 +1,20 @@
+import { test, expect } from "vitest";
+import { loadConfig } from "../src/config.js";
+
+test("loadConfig espone host con default dev-safe 127.0.0.1", () => {
+  expect(loadConfig({})).toMatchObject({ host: "127.0.0.1" });
+});
+
+test("loadConfig rispetta HOST esplicito (necessario in container)", () => {
+  expect(loadConfig({ HOST: "0.0.0.0" })).toMatchObject({ host: "0.0.0.0" });
+});
+
+test("loadConfig merge altri campi con l'host", () => {
+  expect(
+    loadConfig({ HOST: "0.0.0.0", THT_BIN: "/opt/venv/bin/tht", PORT: "9000" })
+  ).toMatchObject({
+    host: "0.0.0.0",
+    thtBin: "/opt/venv/bin/tht",
+    port: 9000,
+  });
+});