Replace details/summary expanders with toggle buttons for list/deck forms

New list, Bulk import, New deck, and Bulk import decks are now proper
buttons. Clicking one toggles the form open (highlighted blue) and
clicking again or cancelling closes it. Only one form open at a time.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/styles.css

@@ -338,6 +338,11 @@ table.results tr:nth-child(even) td { background: #faf7ee; }
 .admin-main h2 { margin: 1.5rem 0 0.5rem; font-size: 1.15rem; }
 .panel { text-align: left; }
 
+/* ---------- toggle button rows (new/bulk import) ---------- */
+.toggle-btns { display: flex; gap: 0.5rem; flex-wrap: wrap; margin-bottom: 0.75rem; }
+.toggle-btns button.active { background: var(--accent); color: #fff; }
+.section-form-title { font-size: 1rem; font-weight: 700; margin: 0 0 0; color: var(--ink); }
+
 /* 2-column layout for wide screens */
 .panel-cols { display: flex; flex-direction: column; gap: 1.5rem; }
 .panel-col { min-width: 0; }