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/ChatShell.tsx

@@ -2,7 +2,7 @@ import { useCallback, useEffect, useState } from "react";
 import { Flex, Box, Center, Loader, Stack, Text, Button } from "@mantine/core";
 import { Sidebar } from "./Sidebar";
 import { ChatPanel } from "./ChatPanel";
-import { api } from "./api";
+import { bus } from "./busService";
 import type { Room, User } from "./types";
 
 export function ChatShell({
@@ -19,7 +19,7 @@ export function ChatShell({
 
   const load = useCallback(() => {
     setLoading(true);
-    api
+    bus
       .listRooms()
       .then((rs) => {
         setRooms(rs);