feat(webui): add Brazilian Portuguese (pt-BR) locale

Translate the WebUI common.json to pt-BR, register the locale in
config.ts (with normalizeLocale rules for "pt", "pt-BR", "pt-PT", ...)
and index.ts resources, and add a Brazilian Portuguese overview
assertion in i18n.test.tsx.

Notes:
- Generic "pt" and any "pt-*" variant resolve to pt-BR. A future
  pt-PT locale can be added without affecting existing users.
- Universally borrowed technical terms (nanobot, BYOK, MCP, JSON,
  URL, Web, Apps when used as a product name, Skills) are kept in
  English, matching the pattern used by es/fr/ja/ko/vi/id.
- Empty-thread greetings, quick-action prompts, and slash command
  descriptions are translated; quick-action prompts are intentionally
  phrased so the agent still receives a clear task spec.

Verified with bun run test (536 passing), bun run lint (clean), and
bun run build (7.18s).

webui/src/i18n/config.ts

@@ -8,6 +8,7 @@ export const supportedLocales = [
   { code: "ja", label: "Japanese", nativeLabel: "日本語" },
   { code: "ko", label: "Korean", nativeLabel: "한국어" },
   { code: "es", label: "Spanish", nativeLabel: "Español" },
+  { code: "pt-BR", label: "Portuguese (Brazil)", nativeLabel: "Português (Brasil)" },
   { code: "vi", label: "Vietnamese", nativeLabel: "Tiếng Việt" },
   { code: "id", label: "Indonesian", nativeLabel: "Bahasa Indonesia" },
 ] as const;
@@ -39,6 +40,9 @@ export function normalizeLocale(
   ) {
     return "zh-TW";
   }
+  if (lower === "pt" || lower.startsWith("pt-")) {
+    return "pt-BR";
+  }
 
   const base = lower.split("-")[0];
   const baseMatch = supportedLocales.find(

webui/src/i18n/index.ts

@@ -19,6 +19,7 @@ import frCommon from "./locales/fr/common.json";
 import jaCommon from "./locales/ja/common.json";
 import koCommon from "./locales/ko/common.json";
 import esCommon from "./locales/es/common.json";
+import ptBRCommon from "./locales/pt-BR/common.json";
 import viCommon from "./locales/vi/common.json";
 import idCommon from "./locales/id/common.json";
 
@@ -30,6 +31,7 @@ export const resources = {
   ja: { common: jaCommon },
   ko: { common: koCommon },
   es: { common: esCommon },
+  "pt-BR": { common: ptBRCommon },
   vi: { common: viCommon },
   id: { common: idCommon },
 } as const;

webui/src/tests/i18n.test.tsx

@@ -311,4 +311,18 @@ describe("webui i18n", () => {
     expect(settings.overview.webSearch).toBe("网页搜索");
     expect(settings.overview.workspace).toBe("工作区");
   });
+
+  it("keeps Brazilian Portuguese settings overview copy localized", () => {
+    const settings = resources["pt-BR"].common.settings;
+    const sidebar = resources["pt-BR"].common.sidebar;
+    const chat = resources["pt-BR"].common.chat;
+
+    expect(sidebar.settings).toBe("Configurações");
+    expect(chat.newChat).toBe("Nova conversa");
+    expect(settings.nav.browser).toBe("Web");
+    expect(settings.sections.webSearch).toBe("Busca na web");
+    expect(settings.byok.tabs.webSearch).toBe("Busca na web");
+    expect(settings.overview.webSearch).toBe("Busca na web");
+    expect(settings.overview.workspace).toBe("Workspace");
+  });
 });