fix: handle os.UserHomeDir errors across all packages

Check os.UserHomeDir() return error instead of silently ignoring it. Prevents operations in wrong directory paths when home directory lookup fails (containers, restricted environments).

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

Author: fullstackjam

internal/brew/brew.go

@@ -553,7 +553,10 @@ func CheckNetwork() error {
 
 func CheckDiskSpace() (float64, error) {
 	var stat syscall.Statfs_t
-	home, _ := os.UserHomeDir()
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return 0, fmt.Errorf("cannot determine home directory: %w", err)
+	}
 	if err := syscall.Statfs(home, &stat); err != nil {
 		return 0, err
 	}

internal/cli/doctor.go

@@ -171,7 +171,14 @@ func checkGit() []checkResult {
 func checkShell() []checkResult {
 	var results []checkResult
 
-	home, _ := os.UserHomeDir()
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return []checkResult{{
+			name:    "Shell",
+			status:  "error",
+			message: "cannot determine home directory",
+		}}
+	}
 	omzPath := filepath.Join(home, ".oh-my-zsh")
 
 	if _, err := os.Stat(omzPath); os.IsNotExist(err) {

internal/dotfiles/dotfiles.go

@@ -15,7 +15,10 @@ func Clone(repoURL string, dryRun bool) error {
 		return nil
 	}
 
-	home, _ := os.UserHomeDir()
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return fmt.Errorf("cannot determine home directory: %w", err)
+	}
 	dotfilesPath := filepath.Join(home, defaultDotfilesDir)
 
 	if _, err := os.Stat(dotfilesPath); err == nil {
@@ -35,7 +38,10 @@ func Clone(repoURL string, dryRun bool) error {
 }
 
 func Link(dryRun bool) error {
-	home, _ := os.UserHomeDir()
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return fmt.Errorf("cannot determine home directory: %w", err)
+	}
 	dotfilesPath := filepath.Join(home, defaultDotfilesDir)
 
 	if _, err := os.Stat(dotfilesPath); os.IsNotExist(err) {
@@ -75,7 +81,10 @@ func linkWithStow(dotfilesPath string, dryRun bool) error {
 		return err
 	}
 
-	home, _ := os.UserHomeDir()
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return fmt.Errorf("cannot determine home directory: %w", err)
+	}
 
 	for _, entry := range entries {
 		if !entry.IsDir() || strings.HasPrefix(entry.Name(), ".") {
@@ -108,7 +117,10 @@ func linkWithStow(dotfilesPath string, dryRun bool) error {
 }
 
 func linkDirect(dotfilesPath string, dryRun bool) error {
-	home, _ := os.UserHomeDir()
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return fmt.Errorf("cannot determine home directory: %w", err)
+	}
 
 	entries, err := os.ReadDir(dotfilesPath)
 	if err != nil {

internal/macos/macos.go

@@ -50,7 +50,10 @@ var DefaultPreferences = []Preference{
 
 func expandHome(path string) string {
 	if strings.HasPrefix(path, "~/") {
-		home, _ := os.UserHomeDir()
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return path
+		}
 		return filepath.Join(home, path[2:])
 	}
 	return path
@@ -89,7 +92,10 @@ func Configure(prefs []Preference, dryRun bool) error {
 }
 
 func CreateScreenshotsDir(dryRun bool) error {
-	home, _ := os.UserHomeDir()
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return fmt.Errorf("cannot determine home directory: %w", err)
+	}
 	dir := filepath.Join(home, "Screenshots")
 
 	if dryRun {
@@ -109,8 +115,9 @@ func RestartAffectedApps(dryRun bool) error {
 			continue
 		}
 
+		// killall returns an error if the app isn't running, which is expected and safe to ignore
 		cmd := exec.Command("killall", app)
-		cmd.Run()
+		cmd.Run() //nolint:errcheck // non-fatal: app may not be running
 	}
 
 	return nil

internal/shell/shell.go

@@ -8,8 +8,11 @@ import (
 )
 
 func IsOhMyZshInstalled() bool {
-	home, _ := os.UserHomeDir()
-	_, err := os.Stat(filepath.Join(home, ".oh-my-zsh"))
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return false
+	}
+	_, err = os.Stat(filepath.Join(home, ".oh-my-zsh"))
 	return err == nil
 }
 
@@ -31,15 +34,21 @@ func InstallOhMyZsh(dryRun bool) error {
 		return err
 	}
 
-	home, _ := os.UserHomeDir()
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return fmt.Errorf("cannot determine home directory: %w", err)
+	}
 	zshrcPath := filepath.Join(home, ".zshrc")
 	os.Remove(zshrcPath)
 
 	return nil
 }
 
 func ConfigureZshrc(dryRun bool) error {
-	home, _ := os.UserHomeDir()
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return fmt.Errorf("cannot determine home directory: %w", err)
+	}
 	zshrcPath := filepath.Join(home, ".zshrc")
 
 	additions := `