Allow creating fields and components inline from dialogs

- Component dialog: 'New...' button next to field selector creates a
  new field definition and immediately adds it to the component form
- Inventory dialog: same pattern for component selector

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

public/templates.html

@@ -336,9 +336,12 @@
 			<div class="form-section-label">Field values</div>
 			<div id="c-field-rows"></div>
 			<div class="form-row add-field-row">
-				<select id="c-add-field-select" class="filter-select">
-					<option value="">— add a field —</option>
-				</select>
+				<div class="input-with-action">
+					<select id="c-add-field-select" class="filter-select">
+						<option value="">— add a field —</option>
+					</select>
+					<button type="button" class="btn btn-secondary btn-sm" id="c-new-field">New…</button>
+				</div>
 			</div>
 			<div class="dialog-actions">
 				<button type="button" class="btn btn-secondary" id="c-cancel">Cancel</button>