feat(bus): complete TypeScript SDK — auth, room envelope, client, transport

Second half of the browser-native bus SDK (issue 0001, Phase 1), making uniweb a
peer of the bus in its own right (like unibus_android) without the Go gateway:

- busauth.ts: NATS user nkey from the Ed25519 key (base32 + crc16, no nkeys dep)
  and control-plane request signing (CanonicalRequest + X-Unibus-* headers).
- room.ts: Policy / Room types (ModeNATS, ModeMatrix).
- client.ts: the pure room ENVELOPE (sealRoomMessage/openRoomMessage — AEAD with
  the subject as AAD, Ed25519 sign, drop on verify/decrypt failure), a transport-
  agnostic BusClient, and a signed ControlPlane HTTP client (fetch room/key/members,
  open the sealed room key locally).
- wstransport.ts: concrete nats.ws WebSocket transport (validated E2E in Phase 3).
- index.ts: public SDK surface.

Parity pinned by vectors from unibus cmd/busvectors (extended with nkey + signed
control-request vectors): 19/19 green. The user's private key signs everything in
the browser and is never sent to any server. Bumps uniweb to 0.2.0.

Remaining for Phase 1 completion: the live nats.ws connection + control-plane,
which need a running unibus with the WebSocket listener — exercised in Phase 3.

web/src/bus/busauth.test.ts

@@ -0,0 +1,41 @@
+// Parity tests for the auth bridge: the browser must produce the same NATS nkey and
+// the same signed control-plane request bytes as the Go client, or it would not
+// authenticate on either plane (issue 0001, Phase 1).
+
+import { describe, it, expect } from "vitest";
+import vectors from "./testdata/vectors.json";
+import { hexToBytes, bytesToHex, base64ToBytes } from "./crypto.js";
+import { nkeyPublic, canonicalRequest, signedHeaders } from "./busauth.js";
+
+describe("NATS nkey encoding", () => {
+  it("derives the same user nkey ('U...') as Go from the Ed25519 pubkey", () => {
+    const v = vectors.nkey;
+    expect(nkeyPublic(hexToBytes(v.sign_pub_hex))).toBe(v.nkey_public);
+  });
+});
+
+describe("control-plane request signing", () => {
+  it("builds the same canonical request bytes as Go", () => {
+    const v = vectors.control_request;
+    const got = canonicalRequest(v.method, v.path, v.ts, v.nonce, hexToBytes(v.body_hex));
+    expect(bytesToHex(got)).toBe(v.canonical_hex);
+  });
+
+  it("produces the same Ed25519 signature as Go (X-Unibus-Sig)", () => {
+    const v = vectors.control_request;
+    const headers = signedHeaders(
+      hexToBytes(vectors.sign.sign_pub_hex),
+      hexToBytes(v.sign_priv_hex),
+      v.method,
+      v.path,
+      v.ts,
+      v.nonce,
+      hexToBytes(v.body_hex),
+    );
+    // X-Unibus-Sig is base64-standard; decode and compare hex to the Go vector.
+    expect(bytesToHex(base64ToBytes(headers["X-Unibus-Sig"]))).toBe(v.sig_hex);
+    expect(headers["X-Unibus-Pub"]).toBe(vectors.sign.sign_pub_hex);
+    expect(headers["X-Unibus-Ts"]).toBe(v.ts);
+    expect(headers["X-Unibus-Nonce"]).toBe(v.nonce);
+  });
+});