refactor(gists): migrate gists.go to NewTool pattern (#1591)

* Migrate context_tools to new ServerTool pattern

Convert GetMe, GetTeams, and GetTeamMembers to use the new typed
dependency injection pattern:
- Functions now take only translations helper, return toolsets.ServerTool
- Handler is generated lazily via deps.GetClient/deps.GetGQLClient
- Tests updated to use serverTool.Handler(deps) pattern
- Fixed error return pattern to return nil for Go error (via result.IsError)

Co-authored-by: Adam Holt <oholt@github.com>

* refactor(gists): migrate gists.go to NewTool pattern

Convert all gist tools (ListGists, GetGist, CreateGist, UpdateGist)
to use the new NewTool helper with ToolDependencies injection.

- Remove getClient parameter from function signatures
- Use deps.GetClient(ctx) inside handlers
- Standardize error handling with utils.NewToolResultErrorFromErr()
- Update all tests to use serverTool.Handler(deps) pattern

Co-authored-by: Adam Holt <omgitsads@users.noreply.github.com>

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Co-authored-by: Adam Holt <oholt@github.com>
Co-authored-by: Adam Holt <omgitsads@users.noreply.github.com>

Author: 3 people