#15044: fix: refresh GitHub Copilot default model list

## Summary - refresh `src/providers/github-copilot-models.ts` default GitHub Copilot model IDs - add modern GPT-5, Claude, Gemini, and Grok model IDs including `gpt-5.3-codex` and `claude-opus-4-6-fast` - remove outdated defaults (`gpt-4o`, `gpt-4.1*`, `o1*`, `o3-mini`) from the Copilot defaults list ## Testing - pnpm test -- src/auto-reply/thinking.test.ts src/agents/model-auth.test.ts Closes #15014 <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This change updates the hard-coded default GitHub Copilot model ID list in `src/providers/github-copilot-models.ts`, adding newer model IDs (GPT‑5, Claude, Gemini, Grok) and removing older defaults. The list is used by the provider layer to decide which Copilot-exposed models are offered/selected by default, so correctness depends on these IDs matching what Copilot actually returns/accepts. <h3>Confidence Score: 5/5</h3> - Mergeable now after aligning default Copilot model IDs across provider entry points. - src/providers/github-copilot-models.ts, extensions/copilot-proxy/index.ts _{Last reviewed commit: 3a6e683} <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->