[📋 ADR]: The driver installs web extensions directly

### Decision record

docs/decisions/17817-driver-extension-install.md (#17817)

### Binding implementation

- [ ] Java — _PR_
- [ ] Python — _PR_
- [ ] Ruby — #17879 (draft)
- [ ] .NET — _PR_
- [ ] JavaScript — _PR_

### Notes

New `installWebExtension` / `uninstallWebExtension` on the driver, returning a `WebExtension` that wraps the id. Deprecating the existing Firefox classic install methods (Decision 2) is part of the work. Chromium install over a Grid goes through the `session/:session_id/se/file` endpoint (Chrome does not accept base64 yet), so an early Chromium binding may land without Grid support.

Start by reading docs/decisions/17817-driver-extension-install.md and the referenced issue #17817. Review the binding implementation checklist and the Ruby draft #17879; done means the listed bindings implement the new installWebExtension and uninstallWebExtension APIs, with the stated Firefox deprecation and Grid limitation addressed.

Written by the indexing model from the issue text.