Google AI Studio API key models not working / missing "Google AI Studio" suffix after latest update

- Copilot Chat Extension Version: 0.57.0
- VS Code Version: 1.129.0
- OS Version: macOS 26.5.2 (Build 25F84)
- Feature: BYOK (Bring Your Own Key) / Custom Models (edit/agent mode)
- Selected model: Gemini models (via Google AI Studio)
- Logs:
Error: (query) Execution failed: Error: Failed to get response from the AI model; retried 5 times (total retry wait time: 6.00 seconds) Last error: non-streaming response body was not valid JSON: expected value at line 1 column 1

17 Jul, 18:08:38 Instructions Discovery Resolved 21 instructions in 25.2ms | loaded: [bloc-event, bloc-listener, bloc-state, bloc, collections, components, constants, dart-general, extensions, failures, firebase-functions, form-inputs, fpdart-preferred-apis, generated-files, injectable, model, page, repository, router, scripts, test] | folders: [/Users/henryadu/.copilot/instructions, /Users/henryadu/.claude/rules, /Users/henryadu/Library/Application Support/Code/User/prompts, /Users/henryadu/StudioProjects/learn_akan/.github/instructions, /Users/henryadu/StudioProjects/learn_akan/.claude/rules]

17 Jul, 18:08:38 Hook Discovery Resolved 3 hooks from 1 files in 25.7ms, skipped 1 | loaded: [workspace-hooks.json] | skipped: [file:///Users/henryadu/.claude/settings.json (claude-hooks-disabled)] | folders: [/Users/henryadu/.copilot/hooks, /Users/henryadu/.claude/settings.json, /Users/henryadu/StudioProjects/learn_akan/.github/hooks, /Users/henryadu/.claude/settings.local.json, /Users/henryadu/StudioProjects/learn_akan/.claude/settings.json]

That's all.

### Description
Yesterday, everything was fine. I could use my Google AI Studio API key to access Gemini models in Copilot Chat. After the update, I can no longer do that.

Previously, the models were suffixed with "Google AI Studio", but now it is just "Google", which leads me to believe that my custom models are not being selected for use. Sometimes I also see "0 credits" below the error message in the chat.

Is this a new thing or a bug? Am I going to have to pay for a Copilot subscription even when using my own API keys? I tried adding a new API key, but they still do not show up. Restarting VS Code did not help, and I have also realized that the tools dropdown is gone. The toggle chat setting is also gone but I see it on a colleagues computer. I'm I part of an A/B test group?

Steps to Reproduce:

1. Configure custom Gemini models using a Google AI Studio API key in Copilot Chat settings.
2. Open Copilot Chat and open the model selection list.
3. Observe that custom "Google AI Studio"-suffixed models are missing, showing only default "Google" models instead, along with occasional "0 credits" errors.
4. Try to submit a chat query and encounter the JSON validation/execution error.
5. Notice that the tools dropdown is missing from the chat UI.