fix: add support for fileOpener in config.json (#911)

This PR introduces the following type:

```typescript
export type FileOpenerScheme = "vscode" | "cursor" | "windsurf";
```

and uses it as the new type for a `fileOpener` option in `config.json`.
If set, this will be used to linkify file annotations in the output
using the URI-based file opener supported in VS Code-based IDEs.

Currently, this does not pass:

Updated `codex-cli/tests/markdown.test.tsx` to verify the new behavior.
Note it required mocking `supports-hyperlinks` and temporarily modifying
`chalk.level` to yield the desired output.

codex-cli/src/components/chat/terminal-chat.tsx

@@ -480,6 +480,7 @@ export default function TerminalChat({
               initialImagePaths,
               flexModeEnabled: Boolean(config.flexMode),
             }}
+            fileOpener={config.fileOpener}
           />
         ) : (
           <Box>