feat(ui): file browser and connection string builder dialogs (#44)

Enter on File Path inputs opens a file browser (load/save, extension
filter, hidden toggle, overwrite confirm). Enter on Connection String
inputs opens a builder for PostgreSQL, MSSQL and SQLite with masked
password/preview, parsing and optional connection test.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

pkg/ui/input_dialogs_test.go

@@ -0,0 +1,63 @@
+package ui
+
+import (
+	"path/filepath"
+	"testing"
+
+	"github.com/rivo/tview"
+)
+
+func newDialogTestEditor() *SchemaEditor {
+	se := &SchemaEditor{app: tview.NewApplication(), pages: tview.NewPages()}
+	se.pages.AddPage("origin", tview.NewBox(), true, true)
+	return se
+}
+
+func TestFileBrowserOpensOnEachMode(t *testing.T) {
+	dir := t.TempDir()
+	touch(t, filepath.Join(dir, "a.dbml"))
+
+	for _, mode := range []FileBrowserMode{FileBrowserLoad, FileBrowserSave} {
+		se := newDialogTestEditor()
+		se.showFileBrowser(FileBrowserConfig{
+			Mode:       mode,
+			StartPath:  filepath.Join(dir, "a.dbml"),
+			Extensions: FormatExtensions("dbml"),
+			ReturnPage: "origin",
+			OnSelect:   func(string) { t.Error("OnSelect must not fire without a selection") },
+		})
+		if !se.pages.HasPage("file-browser") {
+			t.Errorf("mode %d: file-browser page missing", mode)
+		}
+	}
+}
+
+func TestConnStringBuilderOpensForEachKind(t *testing.T) {
+	for _, in := range []string{
+		"",
+		"postgres://u:pw@db:5432/app?sslmode=disable",
+		"sqlserver://sa:pw@sql:1433?database=shop&encrypt=disable",
+		"/tmp/app.db",
+		"postgres://u:p@host:badport/db", // parse error falls back to defaults
+	} {
+		se := newDialogTestEditor()
+		se.showConnStringBuilder(in, ConnPostgres, "origin", func(string) {
+			t.Error("onDone must not fire without Save")
+		})
+		if !se.pages.HasPage(connBuilderPage) {
+			t.Errorf("%q: builder page missing", in)
+		}
+	}
+}
+
+func TestValidateConnFields(t *testing.T) {
+	if validateConnFields(ConnFields{Kind: ConnSQLite}) == "" {
+		t.Error("sqlite without path should be invalid")
+	}
+	if validateConnFields(ConnFields{Kind: ConnPostgres}) == "" {
+		t.Error("postgres without host should be invalid")
+	}
+	if msg := validateConnFields(DefaultConnFields(ConnMSSQL)); msg != "" {
+		t.Errorf("defaults should be valid, got %q", msg)
+	}
+}