chore: modernize Go 1.26, update deps, fix lint issues

- Update Go version from 1.19 to 1.26
- Update all dependencies to latest versions
- Fix staticcheck warnings (unused vars, types, functions)
- Remove unused svgToPng function
- Add GitHub Actions CI workflow

ui/settings.go

@@ -22,7 +22,6 @@ type (
 		AllRepos         selectablelist
 		SelectedRepos    []string
 		cursor           SettingsCursor
-		highlightedEntry int
 		AuthorList       list.Model
 		RepoList         list.Model
 	}