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>

src/plugins/runtime/index.ts

@@ -92,6 +92,14 @@ import {
   sendMessageLine,
 } from "../../line/send.js";
 import { buildTemplateMessageFromPayload } from "../../line/template-messages.js";
+import {
+  listLinqAccountIds,
+  resolveDefaultLinqAccountId,
+  resolveLinqAccount,
+} from "../../linq/accounts.js";
+import { monitorLinqProvider } from "../../linq/monitor.js";
+import { probeLinq } from "../../linq/probe.js";
+import { sendMessageLinq } from "../../linq/send.js";
 import { getChildLogger } from "../../logging.js";
 import { normalizeLogLevel } from "../../logging/levels.js";
 import { convertMarkdownTables } from "../../markdown/tables.js";
@@ -378,6 +386,14 @@ export function createPluginRuntime(): PluginRuntime {
         probeIMessage,
         sendMessageIMessage,
       },
+      linq: {
+        sendMessageLinq,
+        probeLinq,
+        monitorLinqProvider,
+        listLinqAccountIds,
+        resolveDefaultLinqAccountId,
+        resolveLinqAccount,
+      },
       whatsapp: {
         getActiveWebListener,
         getWebAuthAgeMs,