feat(auth): registration mode on ConnectPage (PUBLIC_ENABLE_REGISTRATION)

Add a login/register toggle to ConnectPage backed by a new
useRegisterMutation (register -> /auth/me, mirroring login). The toggle
is shown only when REGISTRATION_ENABLED, resolved with the same
precedence as the API base URL: runtime window.__APP_CONFIG__ >
PUBLIC_ENABLE_REGISTRATION env > default true. The prod runtime-config
script injects the runtime flag. The backend's ALLOW_REGISTRATION stays
the real authority; this only gates the UI. EN/RU strings added.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/api/endpoints/auth.ts

@@ -1,6 +1,12 @@
 import { api } from '../index';
 import { toUser, type RawUser } from '../mappers';
-import type { AuthTokens, LoginRequest, LoginResponse, User } from '../types';
+import type {
+  AuthTokens,
+  LoginRequest,
+  LoginResponse,
+  RegisterRequest,
+  User,
+} from '../types';
 
 /**
  * Auth seam over the backend's wire format: tokens-only login + a separate
@@ -48,6 +54,29 @@ export const authApi = api.injectEndpoints({
         return { data: { user, tokens } };
       },
     }),
+    // Sign-up mirrors login: POST /auth/register returns a token pair (the
+    // backend logs the new account straight in), then GET /auth/me resolves the
+    // user — so the UI gets the same unified { user, tokens } as login.
+    register: build.mutation<LoginResponse, RegisterRequest>({
+      async queryFn(body, _api, _extra, baseQuery) {
+        const tokenRes = await baseQuery({
+          url: '/auth/register',
+          method: 'POST',
+          body,
+        });
+        if (tokenRes.error) return { error: tokenRes.error };
+        const tokens = toTokens(tokenRes.data as RawTokenResponse);
+
+        const meRes = await baseQuery({
+          url: '/auth/me',
+          headers: { Authorization: `Bearer ${tokens.accessToken}` },
+        });
+        if (meRes.error) return { error: meRes.error };
+        const user = toUser(meRes.data as RawUser);
+
+        return { data: { user, tokens } };
+      },
+    }),
     logout: build.mutation<void, { refreshToken: string }>({
       query: ({ refreshToken }) => ({
         url: '/auth/logout',
@@ -74,6 +103,7 @@ export const authApi = api.injectEndpoints({
 
 export const {
   useLoginMutation,
+  useRegisterMutation,
   useLogoutMutation,
   useRefreshTokenMutation,
   useMeQuery,