feat: frontend tests — import/export validator + unit tests + CI integration

- tests/frontend/validate-imports.mjs: 0 errors on 13 modules, 79 exports
  Detects: missing exports, broken imports, const reassignments
- tests/frontend/unit.test.mjs: escapeHtml, state object, module syntax
- Added to CI lint job (runs after Ruff + Mypy)

frontend/js/legacy.js

@@ -44,7 +44,7 @@ function hideProgressBar() {
 // loadVaultSettings
 // =========================================================================
 
-async function loadVaultSettings() {
+export async function loadVaultSettings() {
   try {
     const settings = await api("/api/vaults/settings/all");
     state.vaultSettings = settings;
@@ -84,7 +84,7 @@ function _isInputFocused() {
 // initSearch
 // =========================================================================
 
-function initSearch() {
+export function initSearch() {
   const input = document.getElementById("search-input");
   if (!input) return;
   const caseBtn = document.getElementById("search-case-btn");
@@ -309,7 +309,7 @@ function initSearch() {
 // showWelcome
 // =========================================================================
 
-function showWelcome() {
+export function showWelcome() {
   hideProgressBar();
 
   // Restore or rebuild the dashboard with tabbed sections
@@ -422,7 +422,7 @@ function showWelcome() {
 // goHome
 // =========================================================================
 
-function goHome() {
+export function goHome() {
   const searchInput = document.getElementById("search-input");
   if (searchInput) searchInput.value = "";