Step 7: Add remove command to stop tracking files.

Implements Garden.Remove() which unregisters paths from the manifest,
plus unit tests and the CLI wiring via cobra.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

garden/remove_test.go

@@ -0,0 +1,65 @@
+package garden
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestRemoveTrackedFile(t *testing.T) {
+	root := t.TempDir()
+	repoDir := filepath.Join(root, "repo")
+
+	g, err := Init(repoDir)
+	if err != nil {
+		t.Fatalf("Init: %v", err)
+	}
+
+	// Create and add a file.
+	testFile := filepath.Join(root, "testfile")
+	if err := os.WriteFile(testFile, []byte("hello\n"), 0o644); err != nil {
+		t.Fatalf("writing test file: %v", err)
+	}
+
+	if err := g.Add([]string{testFile}); err != nil {
+		t.Fatalf("Add: %v", err)
+	}
+
+	if len(g.manifest.Files) != 1 {
+		t.Fatalf("expected 1 file after add, got %d", len(g.manifest.Files))
+	}
+
+	// Remove it.
+	if err := g.Remove([]string{testFile}); err != nil {
+		t.Fatalf("Remove: %v", err)
+	}
+
+	if len(g.manifest.Files) != 0 {
+		t.Errorf("expected 0 files after remove, got %d", len(g.manifest.Files))
+	}
+
+	// Verify the manifest was persisted.
+	g2, err := Open(repoDir)
+	if err != nil {
+		t.Fatalf("re-Open: %v", err)
+	}
+	if len(g2.manifest.Files) != 0 {
+		t.Errorf("persisted manifest has %d files, want 0", len(g2.manifest.Files))
+	}
+}
+
+func TestRemoveUntrackedPathErrors(t *testing.T) {
+	root := t.TempDir()
+	repoDir := filepath.Join(root, "repo")
+
+	g, err := Init(repoDir)
+	if err != nil {
+		t.Fatalf("Init: %v", err)
+	}
+
+	// Try removing a path that was never added.
+	bogus := filepath.Join(root, "nonexistent")
+	if err := g.Remove([]string{bogus}); err == nil {
+		t.Fatal("Remove of untracked path should return an error")
+	}
+}