Update deps and boost test coverage from 70.8% to 90%

Update go-git v6, gopsutil v4.26.1, x/term v0.39.0, and transitive deps.
Refactor main() into testable run() function, add injectable processLister
and termWidthFunc for test isolation, and add tests covering detached HEAD,
dirty/clean worktree, empty repo, process listing errors, and terminal
width fallback.

main.go

@@ -99,13 +99,14 @@ func formatOutput(left, right string, padding int) string {
 	return fmt.Sprintf("%s%s%s", left, strings.Repeat(" ", padding), right)
 }
 
-func main() {
-	jsonStr := readInputFromStdin(bufio.NewReader(os.Stdin))
+// run reads JSON from r, builds the statusline, and writes it to w.
+// Returns an error if the input cannot be parsed.
+func run(r *bufio.Reader, w *strings.Builder) error {
+	jsonStr := readInputFromStdin(r)
 
 	data, err := parseStatusInput(jsonStr)
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "Error parsing JSON: %v\n", err)
-		os.Exit(1)
+		return fmt.Errorf("error parsing JSON: %w", err)
 	}
 
 	left, right := buildStatusLine(data)
@@ -121,7 +122,17 @@ func main() {
 	padding := calculatePadding(leftVisible, rightVisible, termWidth)
 	output := formatOutput(left, right, padding)
 
-	fmt.Print(output)
+	w.WriteString(output)
+	return nil
+}
+
+func main() {
+	var out strings.Builder
+	if err := run(bufio.NewReader(os.Stdin), &out); err != nil {
+		fmt.Fprintf(os.Stderr, "%v\n", err)
+		os.Exit(1)
+	}
+	fmt.Print(out.String())
 }
 
 func formatContextInfo(contextSize int, usage *TokenUsage) string {
@@ -136,9 +147,13 @@ func formatContextInfo(contextSize int, usage *TokenUsage) string {
 	return fmt.Sprintf("%dk/%dk", currentK, totalK)
 }
 
+// processLister returns the list of running processes.
+// Replaced in tests to avoid depending on real process state.
+var processLister = process.Processes
+
 func getGiteaStatus() string {
 	// Check if gitea process is running using gopsutil (cross-platform)
-	procs, err := process.Processes()
+	procs, err := processLister()
 	if err != nil {
 		return red + "●" + reset
 	}
@@ -196,8 +211,15 @@ func getGitInfo(cwd string) string {
 	return fmt.Sprintf(" git:(%s)", branch)
 }
 
-func getTerminalWidth() int {
+// termWidthFunc returns the terminal width.
+// Replaced in tests to avoid depending on a real TTY.
+var termWidthFunc = func() (int, error) {
 	width, _, err := term.GetSize(int(os.Stdout.Fd()))
+	return width, err
+}
+
+func getTerminalWidth() int {
+	width, err := termWidthFunc()
 	if err != nil {
 		return 80
 	}