feat: add Linq channel — real iMessage via API, no Mac required

Adds a complete Linq iMessage channel adapter that replaces the existing
iMessage channel's Mac Mini + dedicated Apple ID + SSH wrapper + Full Disk
Access setup with a single API key and phone number.

Core implementation (src/linq/):
- types.ts: Linq webhook event and message types
- accounts.ts: Multi-account resolution from config (env/file/inline token)
- send.ts: REST outbound via Linq Blue V3 API (messages, typing, reactions)
- probe.ts: Health check via GET /v3/phonenumbers
- monitor.ts: Webhook HTTP server with HMAC-SHA256 signature verification,
  replay protection, inbound debouncing, and full dispatch pipeline integration

Extension plugin (extensions/linq/):
- ChannelPlugin implementation with config, security, setup, outbound,
  gateway, and status adapters
- Supports direct and group chats, reactions, and media

Wiring:
- Channel registry, dock, config schema, plugin-sdk exports, and plugin
  runtime all updated to include the new linq channel

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

extensions/linq/index.ts

@@ -0,0 +1,17 @@
+import type { ChannelPlugin, OpenClawPluginApi } from "openclaw/plugin-sdk";
+import { emptyPluginConfigSchema } from "openclaw/plugin-sdk";
+import { linqPlugin } from "./src/channel.js";
+import { setLinqRuntime } from "./src/runtime.js";
+
+const plugin = {
+  id: "linq",
+  name: "Linq",
+  description: "Linq iMessage channel plugin — real iMessage over API, no Mac required",
+  configSchema: emptyPluginConfigSchema(),
+  register(api: OpenClawPluginApi) {
+    setLinqRuntime(api.runtime);
+    api.registerChannel({ plugin: linqPlugin as ChannelPlugin });
+  },
+};
+
+export default plugin;