Delete dead code and stale fixtures, fix config set reindent (closes #70)

Remove the unused internal/models package (and its coverage-only test),
internal/cli/vaultik_snapshot_types.go (a second, dead SnapshotInfo that
shadowed the live type in internal/vaultik), and two fixtures
(test-config.yml, test/integration-config.yml) that use source_dirs and
other keys config.Config no longer has. All confirmed by grep against
origin/next; none has a production consumer.

config set now writes via yaml.NewEncoder with 2-space indent, matching
defaultConfigTemplate, so the first set no longer reindents the file it
promises to preserve. A test covers the round-trip.

Single commit rather than one commit per deletion, per task instruction.
test/integration-config.yml removed per the manager note on the issue.

Model: opus-4-8

internal/cli/config.go

@@ -1,6 +1,7 @@
 package cli
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"os"
@@ -24,6 +25,11 @@ const configSetArgs = 2
 // parent config dirs (e.g. ~/.config) are conventionally traversable.
 const configDirMode = 0o755
 
+// configYAMLIndent matches the 2-space indentation of defaultConfigTemplate,
+// so `config set` writes the file back with the same indentation rather than
+// yaml.Marshal's 4-space default.
+const configYAMLIndent = 2
+
 var (
 	errConfigExists     = errors.New("config file already exists")
 	errEmptyConfig      = errors.New("empty config file")
@@ -381,7 +387,7 @@ Examples:
 				return err
 			}
 
-			out, err := yaml.Marshal(root)
+			out, err := marshalConfigYAML(root)
 			if err != nil {
 				return fmt.Errorf("marshaling config: %w", err)
 			}
@@ -405,6 +411,29 @@ Examples:
 	}
 }
 
+// marshalConfigYAML renders a config document tree with 2-space indentation,
+// matching defaultConfigTemplate. yaml.Marshal defaults to 4 spaces, which
+// would reindent the whole file on the first `config set` despite the promise
+// to preserve formatting.
+func marshalConfigYAML(root *yaml.Node) ([]byte, error) {
+	var buf bytes.Buffer
+
+	enc := yaml.NewEncoder(&buf)
+	enc.SetIndent(configYAMLIndent)
+
+	err := enc.Encode(root)
+	if err != nil {
+		return nil, err
+	}
+
+	err = enc.Close()
+	if err != nil {
+		return nil, err
+	}
+
+	return buf.Bytes(), nil
+}
+
 // loadYAMLFile parses a YAML file into a yaml.Node document tree,
 // which preserves comments and ordering for round-tripping.
 func loadYAMLFile(path string) (*yaml.Node, error) {

internal/cli/config_test.go

@@ -188,6 +188,47 @@ func TestYAMLPathSet(t *testing.T) {
 	}
 }
 
+// TestConfigSetPreservesFormatting asserts the `config set` write path
+// (marshalConfigYAML) round-trips a 2-space-indented file without reindenting
+// it to yaml.Marshal's 4-space default, and keeps comments.
+func TestConfigSetPreservesFormatting(t *testing.T) {
+	t.Parallel()
+
+	root := parseTestYAML(t)
+
+	err := yamlPathSet(root, splitPath("s3.bucket"), "newbucket")
+	if err != nil {
+		t.Fatalf("set s3.bucket: %v", err)
+	}
+
+	out, err := marshalConfigYAML(root)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+
+	text := string(out)
+
+	for _, want := range []string{"# top comment", "# inline comment"} {
+		if !contains(text, want) {
+			t.Errorf("round-tripped YAML dropped comment %q:\n%s", want, text)
+		}
+	}
+
+	// Nested map keys stay at 2-space indent; the bug reindented them to 4.
+	if !contains(text, "\n  bucket: newbucket") {
+		t.Errorf("expected 2-space indent for s3.bucket, got:\n%s", text)
+	}
+
+	if contains(text, "\n    bucket:") {
+		t.Errorf("s3.bucket reindented to 4 spaces:\n%s", text)
+	}
+
+	// Sequence items under a key also stay at 2 spaces.
+	if !contains(text, "\n  - age1aaa") {
+		t.Errorf("expected 2-space indent for sequence item, got:\n%s", text)
+	}
+}
+
 func splitPath(s string) []string {
 	return strings.Split(s, ".")
 }

internal/cli/vaultik_snapshot_types.go

@@ -1,12 +0,0 @@
-package cli
-
-import "time"
-
-// SnapshotInfo represents snapshot information for listing
-//
-//nolint:tagliatelle // snake_case is the established output format
-type SnapshotInfo struct {
-	ID             string    `json:"id"`
-	Timestamp      time.Time `json:"timestamp"`
-	CompressedSize int64     `json:"compressed_size"`
-}