feat(export): add visual word-template settings dialog with graceful default-template fallback

Replaces the two native OS dialogs used to configure the DOCX "Enhanced"
export template (an open-file picker + a message-box question) with a
single in-app modal that shows the currently active template state, per
Task 18's original audit finding that this state was invisible until a
user thought to reopen the menu. Consolidates the "Select Word
Template..."/"Template Settings..." menu items into one "Word Template
Settings..." entry wired to the new dialog; Browse still uses the native
file picker since there is genuinely no bundled folder of templates to
enumerate (confirmed by investigation — see task-18-report.md).

Also fixes a related dangling-reference bug: WordTemplateExporter's
hardcoded default template path (word_template.docx) was deleted from
the repo in an earlier commit, but the code still tried to read it and
threw ENOENT whenever no custom template was selected. convert() now
degrades gracefully by generating a minimal, valid DOCX shell (styles +
numbering matching what markdownToWordXml() already references) instead
of crashing, and the new dialog surfaces this state honestly ("using
default formatting, no default template is bundled") rather than
implying a working default exists.

Out of scope, per explicit instruction: bundling fabricated starter
.docx templates to populate a literal multi-item gallery (rejected as
disproportionate/fake-content scope), and an EPUB template gallery (no
EPUB template mechanism exists anywhere in this codebase to build one
for).

Amit Haridas

src/renderer.js

@@ -1705,6 +1705,7 @@ document.addEventListener('DOMContentLoaded', async () => {
   const pdfEditorModal = new ModalManager('#pdf-editor-dialog');
   const headerFooterModal = new ModalManager('#header-footer-dialog');
   const fieldPickerModal = new ModalManager('#field-picker-dialog');
+  const wordTemplateModal = new ModalManager('#word-template-dialog');
 
   // Make modals globally accessible for functions outside this scope
   window.modals = {
@@ -1718,6 +1719,7 @@ document.addEventListener('DOMContentLoaded', async () => {
     pdfEditorModal,
     headerFooterModal,
     fieldPickerModal,
+    wordTemplateModal,
   };
 
   // Initialize sidebar
@@ -4975,6 +4977,98 @@ window.openHeaderFooterDialog = openHeaderFooterDialog;
 ipcRenderer.on('open-header-footer-dialog', () => {
   openHeaderFooterDialog();
 });
+
+// ================================
+// Word Template Settings Dialog
+// ================================
+//
+// Replaces the two former native OS dialogs ("Select Word Template...",
+// "Template Settings...") with a single in-app modal that shows the
+// currently active template state, instead of that state being invisible
+// until a user thought to reopen a menu item. "Browse..." still triggers
+// a native file picker in the main process — there is no bundled folder
+// of templates to enumerate, so a gallery of multiple templates would
+// require inventing content that doesn't exist; see Task 18 report.
+
+// Tracks the template path chosen via Browse in this dialog session,
+// before it is persisted by Save.
+let pendingWordTemplatePath = null;
+let wordTemplateDefaultAvailable = false;
+
+function openWordTemplateDialog() {
+  window.modals.wordTemplateModal.open();
+  ipcRenderer.send('get-word-template-settings');
+}
+
+function closeWordTemplateDialog() {
+  window.modals.wordTemplateModal.close();
+}
+
+function renderWordTemplateStatus(templateFileName) {
+  const statusEl = document.getElementById('word-template-status');
+  const titleEl = document.getElementById('word-template-status-title');
+  const detailEl = document.getElementById('word-template-status-detail');
+
+  statusEl.classList.remove('wt-status-none', 'wt-status-selected', 'wt-status-missing');
+
+  if (templateFileName) {
+    statusEl.classList.add('wt-status-selected');
+    titleEl.textContent = templateFileName;
+    detailEl.textContent = 'Custom template selected';
+  } else if (wordTemplateDefaultAvailable) {
+    statusEl.classList.add('wt-status-none');
+    titleEl.textContent = 'No template selected';
+    detailEl.textContent = 'Using the bundled default template';
+  } else {
+    statusEl.classList.add('wt-status-missing');
+    titleEl.textContent = 'No template selected';
+    detailEl.textContent = 'Using default formatting (no default template is bundled)';
+  }
+}
+
+// Populate dialog with current settings from main process
+ipcRenderer.on('word-template-settings-data', (event, data) => {
+  pendingWordTemplatePath = data.templatePath || null;
+  wordTemplateDefaultAvailable = !!data.defaultTemplateAvailable;
+  renderWordTemplateStatus(data.templateFileName);
+  document.getElementById('word-template-start-page').value = data.startPage || 3;
+});
+
+// Result of a Browse... click (native picker) or Clear
+ipcRenderer.on('word-template-browsed', (event, data) => {
+  pendingWordTemplatePath = data.templatePath || null;
+  renderWordTemplateStatus(data.templateFileName);
+});
+
+function saveWordTemplateSettings() {
+  const startPageInput = document.getElementById('word-template-start-page');
+  let startPage = parseInt(startPageInput.value, 10);
+  if (!Number.isFinite(startPage) || startPage < 1) startPage = 1;
+  if (startPage > 100) startPage = 100;
+
+  ipcRenderer.send('save-word-template-settings', {
+    templatePath: pendingWordTemplatePath,
+    startPage,
+  });
+  closeWordTemplateDialog();
+}
+
+document.getElementById('word-template-close').addEventListener('click', closeWordTemplateDialog);
+document.getElementById('word-template-cancel').addEventListener('click', closeWordTemplateDialog);
+document.getElementById('word-template-save').addEventListener('click', saveWordTemplateSettings);
+document.getElementById('word-template-browse').addEventListener('click', () => {
+  ipcRenderer.send('browse-word-template');
+});
+document.getElementById('word-template-clear').addEventListener('click', () => {
+  ipcRenderer.send('clear-word-template');
+});
+
+window.openWordTemplateDialog = openWordTemplateDialog;
+
+ipcRenderer.on('open-word-template-dialog', () => {
+  openWordTemplateDialog();
+});
+
 // Command Palette - initialized via CommandPalette class
 // (see DOMContentLoaded handler for registration of commands)