Add golangci-lint config and lint tasks

- Add .golangci.yml with sensible defaults for the project
- Add lint and lint:fix tasks to Taskfile
- Remove unused findGitRoot function
- Apply gofumpt formatting fixes

main.go

@@ -105,7 +105,8 @@ func formatContextInfo(contextSize int, usage *struct {
 	InputTokens          int `json:"input_tokens"`
 	CacheCreationTokens  int `json:"cache_creation_input_tokens"`
 	CacheReadInputTokens int `json:"cache_read_input_tokens"`
-}) string {
+},
+) string {
 	totalK := contextSize / 1000
 
 	if usage == nil {
@@ -177,19 +178,6 @@ func getGitInfo(cwd string) string {
 	return fmt.Sprintf(" git:(%s)", branch)
 }
 
-func findGitRoot(path string) string {
-	for {
-		if _, err := os.Stat(filepath.Join(path, ".git")); err == nil {
-			return path
-		}
-		parent := filepath.Dir(path)
-		if parent == path {
-			return ""
-		}
-		path = parent
-	}
-}
-
 func getTerminalWidth() int {
 	ws, err := unix.IoctlGetWinsize(int(os.Stdout.Fd()), unix.TIOCGWINSZ)
 	if err != nil {