chore: draft unreleased changelog, bump opencode sdk to 1.17.18

Changelog leads with the private relay and the native mobile apps (TestFlight
beta + Android APK links), followed by pairing v2 and the device management,
desktop multi-transport, and chat items; VS Code changelog gets the shared
chat-render entries.

packages/web/package.json

@@ -25,7 +25,7 @@
   "dependencies": {
     "@clack/prompts": "^1.1.0",
     "@octokit/rest": "^22.0.1",
-    "@opencode-ai/sdk": "1.17.12",
+    "@opencode-ai/sdk": "1.17.18",
     "@simplewebauthn/server": "13.3.1",
     "adm-zip": "^0.5.16",
     "better-sqlite3": "^12.10.0",