feat: add OpenCode CLI path override and settings UI

- Add opencodeBinary field to settings and persistence flow
- Introduce OpenCode CLI settings panel with Browse and Save actions

packages/vscode/src/extension.ts

@@ -455,6 +455,7 @@ export async function activate(context: vscode.ExtensionContext) {
         `Working directory: ${workingDirectory}`,
         `Working dir matches workspace: ${workingDirectoryMatchesWorkspace ? 'yes' : 'no'}`,
         `API URL (configured): ${configuredApiUrl || '(none)'}`,
+        `OpenCode binary (configured): ${(vscode.workspace.getConfiguration('openchamber').get<string>('opencodeBinary') || '').trim() || '(none)'}`,
         `API URL (resolved): ${openCodeManager?.getApiUrl() ?? '(none)'}`,
         `API URL path: ${resolvedApiPath || '(none)'}`,
         debug