feat: browser-native client — wire SPA to the SDK, delete the Go gateway

Phase 2 of issue 0001. uniweb becomes a pure frontend (web/ only), like
unibus_android: the SPA talks directly to the bus and the Go gateway is gone.

- busService.ts: the new data layer over the bus SDK, replacing the old api module.
  It holds the user's wallet identity and a connected BusClient IN THE BROWSER and
  opens the session locally — the private key is never sent anywhere (closes the
  gateway-era hole where the browser POSTed its private key to /api/session).
- Wire account/App/ChatShell/ChatPanel/WalletLogin/Recover/Join to busService;
  subscribeRoom replaces the SSE streamRoom; ApiError -> SessionError.
- SDK: ControlPlane.createRoom + listMemberRooms, and fetchRoom mapped to the real
  control-plane wire shape (snake_case, no id) — all verified by the live round-trip.
- Delete cmd/webgw, go.mod, go.sum, src/api.ts and the orphan operator Login. uniweb
  now has zero Go and no dependency on unibus as a module.
- vite: drop the /api proxy, dev server on 5173 to match the bus CORS allowlist; add
  vite-env typings. app.md: lang ts, no uses_functions, e2e_checks are now web-only.
  Bump 0.3.0.

Onboarding by token is now admin-side (the bus has no self-register endpoint; the
gateway only mocked it). tsc + pnpm build + 19/19 unit green.

web/src/Join.tsx

@@ -21,7 +21,7 @@ import {
   IconKey,
   IconShieldLock,
 } from "@tabler/icons-react";
-import { api, ApiError } from "./api";
+import { SessionError } from "./busService";
 import { AuthCard, AuthHeader } from "./AuthShell";
 import type { User } from "./types";
 import { newMnemonic, mnemonicWords } from "./wallet/bip39";
@@ -124,14 +124,21 @@ export function Join({
         setStep("joining");
         setError(null);
         try {
-          // Register the PUBLIC identity with the bus (token authorizes), then
-          // encrypt the private key locally and open the per-user session.
-          const res = await api.register(token, identity.signPub, identity.kexPub);
-          const user = await saveAndOpen(identity, res.handle, password);
+          // The bus has no token-register endpoint (that was a gateway mock): a
+          // browser cannot self-register on an enforce cluster. The identity must be
+          // allow-listed by an admin first. We persist it locally and try to open the
+          // session; if the identity is not yet authorized, openSession fails and we
+          // tell the user to have an admin authorize their public key.
+          const handle = identity.signPub.slice(0, 8);
+          const user = await saveAndOpen(identity, handle, password);
           onJoined(user);
         } catch (e) {
+          const base =
+            e instanceof SessionError || e instanceof Error
+              ? e.message
+              : "No se pudo completar el alta.";
           setError(
-            e instanceof ApiError ? e.message : "No se pudo completar el alta.",
+            `${base}. Pide a un administrador que autorice tu clave pública: ${identity.signPub}`,
           );
           setStep("password");
         }