Add list command to display all tracked entries

Adds Garden.List() method that returns manifest entries, unit tests
for empty and populated repos, and a CLI command that formats output
by entry type (file with hash prefix, link with target, directory).

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

garden/list_test.go

@@ -0,0 +1,67 @@
+package garden
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestListEmpty(t *testing.T) {
+	root := t.TempDir()
+	repoDir := filepath.Join(root, "repo")
+
+	g, err := Init(repoDir)
+	if err != nil {
+		t.Fatalf("Init: %v", err)
+	}
+
+	entries := g.List()
+	if len(entries) != 0 {
+		t.Errorf("expected 0 entries, got %d", len(entries))
+	}
+}
+
+func TestListAfterAdd(t *testing.T) {
+	root := t.TempDir()
+	repoDir := filepath.Join(root, "repo")
+
+	g, err := Init(repoDir)
+	if err != nil {
+		t.Fatalf("Init: %v", err)
+	}
+
+	// Create two files and add them.
+	file1 := filepath.Join(root, "file1")
+	if err := os.WriteFile(file1, []byte("one"), 0o644); err != nil {
+		t.Fatalf("writing file1: %v", err)
+	}
+	file2 := filepath.Join(root, "file2")
+	if err := os.WriteFile(file2, []byte("two"), 0o644); err != nil {
+		t.Fatalf("writing file2: %v", err)
+	}
+
+	if err := g.Add([]string{file1, file2}); err != nil {
+		t.Fatalf("Add: %v", err)
+	}
+
+	entries := g.List()
+	if len(entries) != 2 {
+		t.Fatalf("expected 2 entries, got %d", len(entries))
+	}
+
+	// Verify entries have the correct paths (in tilde form).
+	paths := make(map[string]bool)
+	for _, e := range entries {
+		paths[e.Path] = true
+	}
+
+	want1 := toTildePath(file1)
+	want2 := toTildePath(file2)
+
+	if !paths[want1] {
+		t.Errorf("missing entry for %s", want1)
+	}
+	if !paths[want2] {
+		t.Errorf("missing entry for %s", want2)
+	}
+}