feat(electrobun): multi-machine relay + OTEL telemetry

Multi-machine relay:
- relay-client.ts: WebSocket client for agor-relay with token auth,
  exponential backoff (1s-30s), TCP probe, heartbeat (15s ping)
- machines-store.svelte.ts: remote machine state tracking
- RemoteMachinesSettings.svelte: machine list, add/connect/disconnect UI
- 7 RPC types (remote.connect/disconnect/list/send/status + events)

Telemetry:
- telemetry.ts: OTEL spans + OTLP/HTTP export to Tempo,
  controlled by AGOR_OTLP_ENDPOINT env var
- telemetry-bridge.ts: tel.info/warn/error frontend convenience API
- telemetry.log RPC for frontend→Bun tracing

ui-electrobun/src/shared/pty-rpc-schema.ts

@@ -482,6 +482,78 @@ export type PtyRPCRequests = {
     params: { pluginId: string; filePath: string };
     response: { ok: boolean; content: string; error?: string };
   };
+
+  // ── Remote machine (relay) RPC ────────────────────────────────────────────
+
+  /** Connect to an agor-relay instance. */
+  "remote.connect": {
+    params: { url: string; token: string; label?: string };
+    response: { ok: boolean; machineId?: string; error?: string };
+  };
+  /** Disconnect from a relay instance. */
+  "remote.disconnect": {
+    params: { machineId: string };
+    response: { ok: boolean; error?: string };
+  };
+  /** List all known remote machines with connection status. */
+  "remote.list": {
+    params: Record<string, never>;
+    response: {
+      machines: Array<{
+        machineId: string;
+        label: string;
+        url: string;
+        status: "connecting" | "connected" | "disconnected" | "error";
+        latencyMs: number | null;
+      }>;
+    };
+  };
+  /** Send a command to a connected relay. */
+  "remote.send": {
+    params: { machineId: string; command: string; payload: Record<string, unknown> };
+    response: { ok: boolean; error?: string };
+  };
+  /** Get the status of a specific machine. */
+  "remote.status": {
+    params: { machineId: string };
+    response: {
+      status: "connecting" | "connected" | "disconnected" | "error";
+      latencyMs: number | null;
+      error?: string;
+    };
+  };
+
+  // ── Telemetry RPC ─────────────────────────────────────────────────────────
+
+  /** Log a telemetry event from the frontend. */
+  "telemetry.log": {
+    params: {
+      level: "info" | "warn" | "error";
+      message: string;
+      attributes?: Record<string, string | number | boolean>;
+    };
+    response: { ok: boolean };
+  };
+
+  // ── Updater RPC ──────────────────────────────────────────────────────────
+
+  /** Check GitHub Releases for a newer version. */
+  "updater.check": {
+    params: Record<string, never>;
+    response: {
+      available: boolean;
+      version: string;
+      downloadUrl: string;
+      releaseNotes: string;
+      checkedAt: number;
+      error?: string;
+    };
+  };
+  /** Get the current app version and last check timestamp. */
+  "updater.getVersion": {
+    params: Record<string, never>;
+    response: { version: string; lastCheck: number };
+  };
 };
 
 // ── Messages (Bun → WebView, fire-and-forget) ────────────────────────────────
@@ -518,6 +590,22 @@ export type PtyRPCMessages = {
     inputTokens: number;
     outputTokens: number;
   };
+
+  // ── Remote machine events (Bun → WebView) ────────────────────────────────
+
+  /** Remote relay event forwarded from a connected machine. */
+  "remote.event": {
+    machineId: string;
+    eventType: string;
+    sessionId?: string;
+    payload?: unknown;
+  };
+  /** Remote machine connection status change. */
+  "remote.statusChange": {
+    machineId: string;
+    status: "connecting" | "connected" | "disconnected" | "error";
+    error?: string;
+  };
 };
 
 // ── Combined schema ───────────────────────────────────────────────────────────