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/channels/dock.ts

@@ -18,6 +18,7 @@ import {
 } from "../config/group-policy.js";
 import { resolveDiscordAccount } from "../discord/accounts.js";
 import { resolveIMessageAccount } from "../imessage/accounts.js";
+import { resolveLinqAccount } from "../linq/accounts.js";
 import { requireActivePluginRegistry } from "../plugins/runtime.js";
 import { normalizeAccountId } from "../routing/session-key.js";
 import { resolveSignalAccount } from "../signal/accounts.js";
@@ -450,6 +451,23 @@ const DOCKS: Record<ChatChannelId, ChannelDock> = {
         buildDirectOrGroupThreadToolContext({ context, hasRepliedRef }),
     },
   },
+  linq: {
+    id: "linq",
+    capabilities: {
+      chatTypes: ["direct", "group"],
+      reactions: true,
+      media: true,
+    },
+    outbound: { textChunkLimit: 4000 },
+    config: {
+      resolveAllowFrom: ({ cfg, accountId }) =>
+        (resolveLinqAccount({ cfg, accountId }).config.allowFrom ?? []).map((entry) =>
+          String(entry),
+        ),
+      formatAllowFrom: ({ allowFrom }) =>
+        allowFrom.map((entry) => String(entry).trim()).filter(Boolean),
+    },
+  },
 };
 
 function buildDockFromPlugin(plugin: ChannelPlugin): ChannelDock {