feat: add private relay for end-to-end-encrypted remote access (#2087)

Adds OpenChamber Relay — an opt-in way to reach an instance from a phone,
browser, or another desktop from anywhere, with no open inbound ports, no
tunnel, and no shared LAN. The instance dials outbound to a relay; all app
traffic (HTTP, the event stream, terminal, dictation) is multiplexed and
encrypted through a single connection per client, so the relay only ever
forwards opaque ciphertext.

Transport
- End-to-end-encrypted channel over WebCrypto (ECDH P-256 -> HKDF ->
  AES-256-GCM) with a capability-negotiated handshake and a small
  HTTP/SSE/WebSocket multiplexing protocol. A byte-compatible JS host mirror
  is cross-checked by tests.
- Host: outbound connection manager, per-client tunnel dispatcher to the local
  server over loopback, reuse of the existing instance identity key, and
  management routes. Disabled by default; explicit opt-in.
- Client: plugs into the existing runtime layer (runtime-fetch/-url/-switch/
  -auth, event pipeline, terminal, dictation) so features work over the relay
  unchanged; direct-URL and Electron realtime-proxy paths are untouched.

Pairing & UX
- Relay section in Settings -> Remote Instances (live status, QR/link pairing,
  revocation via the existing client-token list) and the mobile connect flow.
- Frame batching and idle-gated keepalive keep tunnel message volume low
  without affecting streaming smoothness.

Security
- The tunnel is transport only; the server authenticates every tunneled
  request exactly as for a direct remote client.
  fragments only. The relay stores no keys, tokens, or payloads.

Operability
- The endpoint can be pinned to a self-hosted rel
  paired clients inherit it from the offer automatically.
- Relay module DOCUMENTATION.md and a relay-trans
  invariants that future WebSocket/streaming changes must follow.

The relay transport is complete and tested; the UI for enabling and pairing
is gated behind openchamber_relay_gate and stays

packages/ui/src/apps/mobileQrScan.ts

@@ -9,10 +9,19 @@
 // at runtime instead of importing the package so the web build stays dependency-free
 // and the browser-hosted mobile UI degrades to `unsupported` cleanly.
 
+import { parseRelayOfferUrl } from '@/lib/relay/offer';
+
+import type { MobileRelayConfig } from './mobileConnections';
+
 export type MobileConnectionPayload = {
   url: string;
   clientToken?: string;
   label?: string;
+  // Present when the payload is a relay pairing offer (openchamber://connect?v=1&mode=relay#offer=...).
+  // `url` then holds the raw offer link so form fields and connect() can round-trip it.
+  relay?: MobileRelayConfig;
+  // One-time relay authorization grant from the offer. Never persisted.
+  relayGrant?: string;
 };
 
 export type QrScanResult =
@@ -108,6 +117,23 @@ export const parseConnectionPayload = (raw: string): MobileConnectionPayload | n
   if (!trimmed) return null;
 
   if (/^openchamber:\/\//i.test(trimmed)) {
+    // Relay pairing offers are a strict superset format (mode=relay + fragment
+    // payload); try them first. Direct pairing links (?server=...) never match
+    // the relay parser, so existing payloads are untouched.
+    const offer = parseRelayOfferUrl(trimmed);
+    if (offer) {
+      return {
+        url: trimmed,
+        clientToken: offer.token,
+        label: offer.label,
+        relay: {
+          relayUrl: offer.relayUrl,
+          serverId: offer.serverId,
+          hostEncPubJwk: offer.hostEncPubJwk,
+        },
+        relayGrant: offer.grant,
+      };
+    }
     try {
       const parsed = new URL(trimmed);
       const server = parsed.searchParams.get('server')?.trim();