Badges: template controls cfg, collapsible form sections, navigation polish

- badge_template_form: fix default field visibility (location off render, pronouns/leads excluded from controls); fix duplicate QR checkboxes by removing orphan show_qr_front/back state vars; reorganize Advanced cfg_json into labeled sub-groups; make all 5 non-Advanced sections collapsible (general starts open, rest collapsed)
- print_controls: add DEFAULT_SHOWN constant so field_shown() uses explicit whitelist fallback instead of showing all fields when no controls_cfg is set
- badges config +page: add Templates navigation button in header (FileText icon)
- templates +page: add back-nav header with ArrowLeft to badges/config, Settings icon, page title

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

src/routes/events/[event_id]/(badges)/badges/config/+page.svelte

@@ -26,6 +26,7 @@ import {
     Check,
     ChevronDown,
     ChevronUp,
+    FileText,
     Lock,
     Save,
     Settings
@@ -270,6 +271,11 @@ function toggle(key: string) {
                 <Settings size="1.2em" class="text-primary-500" />
                 <h1 class="text-xl font-bold">Badges Config</h1>
             </div>
+            <a href="/events/{event_id}/templates"
+                class="btn btn-sm preset-tonal-surface"
+                title="Manage Badge Templates">
+                <FileText size="1em" class="mr-1" /> Templates
+            </a>
             <div class="flex items-center gap-2">
                 {#if save_status === 'success'}
                     <span class="badge preset-tonal-success flex items-center gap-1">