#21034: docs(providers): add back link to Github Copilot

## Summary - Problem: Link to GitHub Copilot is accidentally deleted - Why it matters: Unsearchable GitHub Copilot doc - What changed: add back GitHub Copilot to providers doc - What did NOT change (scope boundary): ## Change Type (select all) - [ ] Bug fix - [ ] Feature - [ ] Refactor - [x] Docs - [ ] Security hardening - [ ] Chore/infra ## Scope (select all touched areas) - [ ] Gateway / orchestration - [ ] Skills / tool execution - [ ] Auth / tokens - [ ] Memory / storage - [ ] Integrations - [ ] API / contracts - [ ] UI / DX - [ ] CI/CD / infra ## Linked Issue/PR - Closes # - Related #1120 ## User-visible / Behavior Changes `None` ## Security Impact (required) - New permissions/capabilities? (`No`) - Secrets/tokens handling changed? (`No`) - New/changed network calls? (`No`) - Command/tool execution surface changed? (`No`) - Data access scope changed? (`No`) - If any `Yes`, explain risk + mitigation: ## Repro + Verification ### Environment - OS: - Runtime/container: - Model/provider: - Integration/channel (if any): - Relevant config (redacted): ### Steps 1. 2. 3. ### Expected - ### Actual - ## Evidence Attach at least one: - [ ] Failing test/log before + passing after - [ ] Trace/log snippets - [ ] Screenshot/recording - [ ] Perf numbers (if relevant) ## Human Verification (required) What you personally verified (not just CI), and how: - Verified scenarios: - Edge cases checked: - What you did **not** verify: ## Compatibility / Migration - Backward compatible? (`Yes/No`) - Config/env changes? (`Yes/No`) - Migration needed? (`Yes/No`) - If yes, exact upgrade steps: ## Failure Recovery (if this breaks) - How to disable/revert this change quickly: - Files/config to restore: - Known bad symptoms reviewers should watch for: ## Risks and Mitigations List only real risks for this PR. Add/remove entries as needed. If none, write `None`. - Risk: - Mitigation: <!-- greptile_comment --> <h3>Greptile Summary</h3> This PR restores the GitHub Copilot provider link to the documentation index. The link was added in the correct alphabetical position (between Anthropic and Qwen) in both English and Chinese versions. The target documentation files exist at `/docs/providers/github-copilot.md`, confirming the link is valid and functional. <h3>Confidence Score: 5/5</h3> - This PR is completely safe to merge with no risk - This is a pure documentation change that adds back a single link. The target documentation files exist, the link syntax is correct, and the placement is alphabetically appropriate. No code logic, no dependencies, no security implications. - No files require special attention _{Last reviewed commit: b03c07e} <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->