fix: make shellenv OS-specific and fix Windows binary path

Two critical fixes for e2e test failures:

1. **Make shellenv output OS-specific** (main.go:628-676)
   - Windows: Output only PowerShell code
   - Unix (macOS/Linux): Output only bash/zsh code
   - Previous approach mixed PowerShell and bash syntax causing parse errors
   - PowerShell syntax `if ($PSVersionTable)` broke bash/zsh sourcing
   - Error: "Auto-cd failed" because wt function wasn't defined

2. **Fix Windows binary path** (e2e_test.go:245-249)
   - Add .exe extension to binary name on Windows
   - Detect Windows via filepath.Separator == '\\\\'
   - Previous code built "wt.exe" but returned "wt" path
   - Error: "Cannot bind argument to parameter 'Command' because it is null"
   - PowerShell couldn't find/execute the binary

Root causes:
- macOS tests failed because shellenv output contained unparseable PowerShell syntax
- Windows tests failed because binary path was missing .exe extension

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: timvw

e2e_test.go

@@ -242,7 +242,13 @@ func setupTestRepo(t *testing.T, repoDir string) {
 func buildWtBinary(t *testing.T, tmpDir string) string {
 	t.Helper()
 
-	binaryPath := filepath.Join(tmpDir, "wt")
+	binaryName := "wt"
+	// On Windows, executables need .exe extension
+	if filepath.Separator == '\\' {
+		binaryName = "wt.exe"
+	}
+
+	binaryPath := filepath.Join(tmpDir, binaryName)
 	cmd := exec.Command("go", "build", "-o", binaryPath, ".")
 	if output, err := cmd.CombinedOutput(); err != nil {
 		t.Fatalf("Failed to build wt binary: %v\nOutput: %s", err, output)

main.go

@@ -6,6 +6,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"regexp"
+	"runtime"
 	"strings"
 
 	"github.com/manifoldco/promptui"
@@ -626,52 +627,57 @@ This enables:
 - Automatic cd to worktree after checkout/create/pr/mr commands
 - Tab completion for commands and branch names`,
 	Run: func(cmd *cobra.Command, args []string) {
-		fmt.Print(`# PowerShell integration
-if ($PSVersionTable) {
-    function wt {
-        $output = & (Get-Command -CommandType Application wt).Source @args
-        $exitCode = $LASTEXITCODE
-        Write-Output $output
-        if ($exitCode -eq 0) {
-            $cdPath = $output | Select-String -Pattern "^TREE_ME_CD:" | ForEach-Object { $_.Line.Substring(11) }
-            if ($cdPath) {
-                Set-Location $cdPath
-            }
+		// Output OS-specific shell integration
+		// On Windows, default to PowerShell. On Unix, output bash/zsh.
+		if runtime.GOOS == "windows" {
+			// PowerShell integration for Windows
+			fmt.Print(`# PowerShell integration
+function wt {
+    $output = & (Get-Command -CommandType Application wt).Source @args
+    $exitCode = $LASTEXITCODE
+    Write-Output $output
+    if ($exitCode -eq 0) {
+        $cdPath = $output | Select-String -Pattern "^TREE_ME_CD:" | ForEach-Object { $_.Line.Substring(11) }
+        if ($cdPath) {
+            Set-Location $cdPath
         }
-        $global:LASTEXITCODE = $exitCode
     }
+    $global:LASTEXITCODE = $exitCode
+}
 
-    # PowerShell completion
-    Register-ArgumentCompleter -CommandName wt -ScriptBlock {
-        param($commandName, $wordToComplete, $commandAst, $fakeBoundParameters)
+# PowerShell completion
+Register-ArgumentCompleter -CommandName wt -ScriptBlock {
+    param($commandName, $wordToComplete, $commandAst, $fakeBoundParameters)
 
-        $commands = @('checkout', 'co', 'create', 'pr', 'mr', 'list', 'ls', 'remove', 'rm', 'prune', 'help', 'shellenv')
+    $commands = @('checkout', 'co', 'create', 'pr', 'mr', 'list', 'ls', 'remove', 'rm', 'prune', 'help', 'shellenv')
 
-        # Get the position in the command line
-        $position = $commandAst.CommandElements.Count - 1
+    # Get the position in the command line
+    $position = $commandAst.CommandElements.Count - 1
 
-        if ($position -eq 0) {
-            # Complete commands
-            $commands | Where-Object { $_ -like "$wordToComplete*" } | ForEach-Object {
-                [System.Management.Automation.CompletionResult]::new($_, $_, 'ParameterValue', $_)
+    if ($position -eq 0) {
+        # Complete commands
+        $commands | Where-Object { $_ -like "$wordToComplete*" } | ForEach-Object {
+            [System.Management.Automation.CompletionResult]::new($_, $_, 'ParameterValue', $_)
+        }
+    } elseif ($position -eq 1) {
+        $subCommand = $commandAst.CommandElements[1].Value
+        if ($subCommand -in @('checkout', 'co', 'remove', 'rm')) {
+            # Complete branch names from worktree list
+            $branches = git worktree list 2>$null | Select-Object -Skip 1 | ForEach-Object {
+                if ($_ -match '\[([^\]]+)\]') { $matches[1] }
             }
-        } elseif ($position -eq 1) {
-            $subCommand = $commandAst.CommandElements[1].Value
-            if ($subCommand -in @('checkout', 'co', 'remove', 'rm')) {
-                # Complete branch names from worktree list
-                $branches = git worktree list 2>$null | Select-Object -Skip 1 | ForEach-Object {
-                    if ($_ -match '\[([^\]]+)\]') { $matches[1] }
-                }
-                $branches | Where-Object { $_ -like "$wordToComplete*" } | ForEach-Object {
-                    [System.Management.Automation.CompletionResult]::new($_, $_, 'ParameterValue', $_)
-                }
+            $branches | Where-Object { $_ -like "$wordToComplete*" } | ForEach-Object {
+                [System.Management.Automation.CompletionResult]::new($_, $_, 'ParameterValue', $_)
             }
         }
     }
-    return
 }
+`)
+			return
+		}
 
-wt() {
+		// Bash/Zsh integration for Unix systems
+		fmt.Print(`wt() {
     # All commands (including interactive) need output capture for auto-cd
     local output
     output=$(command wt "$@")