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.

package.json

@@ -107,7 +107,7 @@
     "@heroui/theme": "^2.4.23",
     "@lezer/highlight": "^1.2.3",
     "@octokit/rest": "^22.0.1",
-    "@opencode-ai/sdk": "1.17.12",
+    "@opencode-ai/sdk": "1.17.18",
     "@radix-ui/react-collapsible": "^1.1.12",
     "@radix-ui/react-dialog": "^1.1.15",
     "@radix-ui/react-dropdown-menu": "^2.1.16",