feat(channels): add Synology Chat native channel (#23012)

* feat(channels): add Synology Chat native channel

Webhook-based integration with Synology NAS Chat (DSM 7+).
Supports outgoing webhooks, incoming messages, multi-account,
DM policies, rate limiting, and input sanitization.

- HMAC-based constant-time token validation
- Configurable SSL verification (allowInsecureSsl) for self-signed NAS certs
- 54 unit tests across 5 test suites
- Follows the same ChannelPlugin pattern as LINE/Discord/Telegram

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

* feat(synology-chat): add pairing, warnings, messaging, agent hints

- Enable media capability (file_url already supported by client)
- Add pairing.notifyApproval to message approved users
- Add security.collectWarnings for missing token/URL, insecure SSL, open DM policy
- Add messaging.normalizeTarget and targetResolver for user ID resolution
- Add directory stubs (self, listPeers, listGroups)
- Add agentPrompt.messageToolHints with Synology Chat formatting guide
- 63 tests (up from 54), all passing

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

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

extensions/synology-chat/package.json

@@ -0,0 +1,29 @@
+{
+  "name": "@openclaw/synology-chat",
+  "version": "2026.2.22",
+  "private": true,
+  "description": "Synology Chat channel plugin for OpenClaw",
+  "type": "module",
+  "devDependencies": {
+    "openclaw": "workspace:*"
+  },
+  "openclaw": {
+    "extensions": [
+      "./index.ts"
+    ],
+    "channel": {
+      "id": "synology-chat",
+      "label": "Synology Chat",
+      "selectionLabel": "Synology Chat (Webhook)",
+      "docsPath": "/channels/synology-chat",
+      "docsLabel": "synology-chat",
+      "blurb": "Connect your Synology NAS Chat to OpenClaw with full agent capabilities.",
+      "order": 90
+    },
+    "install": {
+      "npmSpec": "@openclaw/synology-chat",
+      "localPath": "extensions/synology-chat",
+      "defaultChoice": "npm"
+    }
+  }
+}