Fix sidebar sections, terminal resize, and improve .gitignore

Sidebar:
- Add -webkit-user-select: none to section headers (WebKit prefix)
- Fix class mismatches: sidebar-section-chevron → section-chevron,
  sidebar-section-count → section-count, sidebar-section-list → sidebar-list

Terminal resize:
- Poll container dimensions after creation — retry fit every 50ms
  until container has non-zero width/height (up to 20 attempts)
- Add flex: 1 and min-height: 0 to .xterm inside session-panel
  so it participates in flex layout correctly

.gitignore:
- Comprehensive rewrite covering build output, Wails bindings,
  frontend libs, IDE files, OS metadata, and application data

frontend/src/js/sidebar.js

@@ -113,16 +113,16 @@ class Sidebar {
         // Section header
         const header = createElement('div', 'sidebar-section-header');
         header.innerHTML = `
-            <span class="sidebar-section-chevron ${isCollapsed ? 'collapsed' : ''}">${isCollapsed ? '▸' : '▾'}</span>
-            <span class="sidebar-section-title">${escapeHtml(title)}</span>
-            <span class="sidebar-section-count">${profiles.length}</span>
+            <span class="section-chevron ${isCollapsed ? 'collapsed' : ''}">${isCollapsed ? '▸' : '▾'}</span>
+            <span>${escapeHtml(title)}</span>
+            <span class="section-count">${profiles.length}</span>
         `;
         header.addEventListener('click', () => this.toggleSection(key));
         section.appendChild(header);
 
         // Items
         if (!isCollapsed) {
-            const list = createElement('div', 'sidebar-section-list');
+            const list = createElement('div', 'sidebar-list');
             for (const profile of profiles) {
                 list.appendChild(this.renderProfileItem(profile));
             }