fix: create .git/hooks directory if it doesn't exist (#6)

## Problem

`roborev init` fails when the `.git/hooks` directory doesn't exist:

```
Error: install hook: open /path/to/repo/.git/hooks/post-commit: no such file or directory
```

This happens in repositories where the hooks directory has been removed
or was never created.

## Solution

Added `os.MkdirAll` to create the `.git/hooks` directory before
attempting to write the post-commit hook file.

## Changes

- **`cmd/roborev/main.go`**: Added hooks directory creation in both
`initCmd()` and `installHookCmd()`
- **`cmd/roborev/main_test.go`**: Added comprehensive test
`TestInitCmdCreatesHooksDirectory` that:
  - Creates a git repo without a hooks directory
  - Verifies `roborev init` succeeds
  - Confirms the hooks directory and post-commit hook are created
  - Validates hook is executable

## Testing

All existing tests pass, and the new test confirms the fix:

```bash
go test ./cmd/roborev/...
# ok  	github.com/wesm/roborev/cmd/roborev	3.617s
```

The fix follows TDD methodology:
1. ✅ Wrote failing test first
2. ✅ Implemented minimal fix
3. ✅ Verified test passes

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: sinzin91

cmd/roborev/main.go

@@ -260,6 +260,12 @@ func initCmd() *cobra.Command {
 # RoboRev post-commit hook - auto-reviews every commit
 roborev enqueue --sha HEAD 2>/dev/null &
 `
+			// Ensure hooks directory exists
+			hooksDir := filepath.Join(root, ".git", "hooks")
+			if err := os.MkdirAll(hooksDir, 0755); err != nil {
+				return fmt.Errorf("create hooks directory: %w", err)
+			}
+
 			// Check for existing hook
 			if existing, err := os.ReadFile(hookPath); err == nil {
 				if !strings.Contains(string(existing), "roborev") {
@@ -706,6 +712,12 @@ func installHookCmd() *cobra.Command {
 				return fmt.Errorf("hook already exists at %s (use --force to overwrite)", hookPath)
 			}
 
+			// Ensure hooks directory exists
+			hooksDir := filepath.Join(root, ".git", "hooks")
+			if err := os.MkdirAll(hooksDir, 0755); err != nil {
+				return fmt.Errorf("create hooks directory: %w", err)
+			}
+
 			hookContent := `#!/bin/sh
 # RoboRev post-commit hook - auto-reviews every commit
 roborev enqueue --sha HEAD 2>/dev/null &

cmd/roborev/main_test.go

@@ -306,3 +306,98 @@ func TestUninstallHookCmd(t *testing.T) {
 		}
 	})
 }
+
+func TestInitCmdCreatesHooksDirectory(t *testing.T) {
+	// Override HOME to prevent reading real daemon.json
+	tmpHome := t.TempDir()
+	origHome := os.Getenv("HOME")
+	os.Setenv("HOME", tmpHome)
+	defer os.Setenv("HOME", origHome)
+
+	// Create a temp git repo WITHOUT a hooks directory
+	tmpDir := t.TempDir()
+
+	// Initialize git repo
+	cmd := exec.Command("git", "init")
+	cmd.Dir = tmpDir
+	cmd.Env = append(os.Environ(),
+		"HOME="+tmpHome,
+		"GIT_AUTHOR_NAME=Test",
+		"GIT_AUTHOR_EMAIL=test@test.com",
+		"GIT_COMMITTER_NAME=Test",
+		"GIT_COMMITTER_EMAIL=test@test.com",
+	)
+	if out, err := cmd.CombinedOutput(); err != nil {
+		t.Fatalf("git init failed: %v\n%s", err, out)
+	}
+
+	// Remove .git/hooks directory to simulate the problematic scenario
+	hooksDir := filepath.Join(tmpDir, ".git", "hooks")
+	if err := os.RemoveAll(hooksDir); err != nil {
+		t.Fatalf("Failed to remove hooks directory: %v", err)
+	}
+
+	// Verify hooks directory doesn't exist
+	if _, err := os.Stat(hooksDir); !os.IsNotExist(err) {
+		t.Fatal("hooks directory should not exist before test")
+	}
+
+	// Create a roborevd binary in PATH for the test (init tries to start daemon)
+	// We'll use a fake one that does nothing
+	binDir := filepath.Join(tmpHome, "bin")
+	if err := os.MkdirAll(binDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+	fakeDaemon := filepath.Join(binDir, "roborevd")
+	fakeScript := "#!/bin/sh\nexit 0\n"
+	if err := os.WriteFile(fakeDaemon, []byte(fakeScript), 0755); err != nil {
+		t.Fatal(err)
+	}
+	origPath := os.Getenv("PATH")
+	os.Setenv("PATH", binDir+":"+origPath)
+	defer os.Setenv("PATH", origPath)
+
+	// Run init command
+	cmd = exec.Command("go", "run", "./cmd/roborev", "init", "--agent", "test")
+	cmd.Dir = filepath.Join(tmpDir, "..", "..", "..") // Go back to project root
+	cmd.Env = append(os.Environ(),
+		"HOME="+tmpHome,
+		"PATH="+binDir+":"+origPath,
+	)
+	// Change to the test repo directory before running
+	origWd, _ := os.Getwd()
+	if err := os.Chdir(tmpDir); err != nil {
+		t.Fatal(err)
+	}
+	defer os.Chdir(origWd)
+
+	// Build init command
+	initCommand := initCmd()
+	initCommand.SetArgs([]string{"--agent", "test"})
+	err := initCommand.Execute()
+
+	// Should succeed (not fail with "no such file or directory")
+	if err != nil {
+		t.Fatalf("init command failed: %v", err)
+	}
+
+	// Verify hooks directory was created
+	if _, err := os.Stat(hooksDir); os.IsNotExist(err) {
+		t.Error("hooks directory was not created")
+	}
+
+	// Verify hook file was created
+	hookPath := filepath.Join(hooksDir, "post-commit")
+	if _, err := os.Stat(hookPath); os.IsNotExist(err) {
+		t.Error("post-commit hook was not created")
+	}
+
+	// Verify hook is executable
+	info, err := os.Stat(hookPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if info.Mode()&0111 == 0 {
+		t.Error("post-commit hook is not executable")
+	}
+}