fix(archive): correct flat-layout path and entry-count wording

Drop the phantom <basename>/ level for flat-layout installs (profileDir == root), say "entries" not "files" (count is per source path), and add ZipDir/Unzip (>1MB, empty, Zip-Slip) + flat-layout tests.

browser/archive.go

@@ -22,7 +22,7 @@ type Archivable interface {
 // BuildArchive packs each browser's decryption-relevant files into a zip whose internal layout is
 // <browser-key>/<User Data layout>, so a restore can re-expand it and decrypt with a keys.json. Files
 // are staged through a locked-file session first because Windows holds exclusive SQLite locks. Returns
-// the number of files captured.
+// the number of source entries staged (a directory source counts once).
 func BuildArchive(browsers []Browser, categories []types.Category, outPath string) (int, error) {
 	session, err := filemanager.NewSession()
 	if err != nil {

browser/chromium/archive.go

@@ -32,7 +32,12 @@ func (b *Browser) ArchiveSources(categories []types.Category) []ArchiveSource {
 		}
 	}
 	for _, p := range b.profiles {
-		profileRel := filepath.Base(p.profileDir)
+		// Flat-layout installs hold data directly under UserDataDir (profileDir == root); skip the
+		// basename so the archive matches the real layout instead of inserting a phantom level.
+		profileRel := ""
+		if p.profileDir != b.cfg.UserDataDir {
+			profileRel = filepath.Base(p.profileDir)
+		}
 		for _, marker := range profileMarkers {
 			abs := filepath.Join(p.profileDir, marker)
 			if fileutil.FileExists(abs) {

browser/chromium/archive_test.go

@@ -56,3 +56,33 @@ func TestArchiveSources_ForwardSlashLayout(t *testing.T) {
 		t.Errorf("missing Local State entry (User Data root file), got %+v", srcs)
 	}
 }
+
+func TestArchiveSources_FlatLayoutNoExtraLevel(t *testing.T) {
+	// Flat-layout install: data lives directly under UserDataDir with no Default/ subdir, so
+	// discoverProfiles falls back to UserDataDir itself as the profile (profileDir == root).
+	udd := t.TempDir()
+	if err := os.WriteFile(filepath.Join(udd, "History"), []byte("x"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	b, err := NewBrowser(types.BrowserConfig{Key: "opera", Name: "opera", Kind: types.Chromium, UserDataDir: udd})
+	if err != nil || b == nil {
+		t.Fatalf("NewBrowser: b=%v err=%v", b, err)
+	}
+
+	srcs := b.ArchiveSources([]types.Category{types.History})
+
+	phantom := filepath.Base(udd) + "/"
+	var gotHistory bool
+	for _, s := range srcs {
+		if strings.HasPrefix(s.LayoutRel, phantom) {
+			t.Errorf("flat layout must not insert a %q level, got %q", phantom, s.LayoutRel)
+		}
+		if s.LayoutRel == "History" {
+			gotHistory = true
+		}
+	}
+	if !gotHistory {
+		t.Errorf("expected History at archive root, got %+v", srcs)
+	}
+}