fix: file display, persistence, PDF support and save error handling

- Add file proxy route in maker blueprint (X-API-Key auth for browser requests)
- Persist file_path/annotations_json to DB via RecipeCreate/RecipeUpdate schemas
- Fix canvas sizing using grandparent container instead of Fabric.js wrapper div
- Defer canvas init with requestAnimationFrame for x-show timing
- Add PDF.js support in annotation-editor and annotation-viewer
- Fix annotations_json double-serialization (parse string to object before send)
- Handle FastAPI 422 validation error arrays in api_client and JS error display
- Update template URLs to use /maker/api/files/ proxy path

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

client/templates/maker/recipe_preview.html

@@ -207,7 +207,7 @@
           <div class="annotation-container"
                x-data="annotationViewer()"
                x-init="
-                 imageUrl = '/api/files/{{ task.file_path }}';
+                 imageUrl = '/maker/api/files/{{ task.file_path }}';
                  annotations = {{ task.annotations_json|default('null')|tojson }};
                  $nextTick(() => init());
                ">
@@ -225,7 +225,7 @@
             <p class="text-sm font-medium text-[var(--text-primary)]">{{ _('Documento PDF allegato') }}</p>
             <p class="text-xs text-[var(--text-muted)]">{{ task.file_path }}</p>
           </div>
-          <a href="/api/files/{{ task.file_path }}"
+          <a href="/maker/api/files/{{ task.file_path }}"
              target="_blank"
              class="btn btn-secondary text-xs gap-1.5">
             <svg class="w-3.5 h-3.5" fill="none" stroke="currentColor" stroke-width="2" viewBox="0 0 24 24">
@@ -424,7 +424,11 @@
 {% endblock %}
 
 {% block extra_js %}
-<script src="{{ url_for('static', filename='js/annotation-viewer.js') }}"></script>
+<script src="https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.min.js"></script>
+<script>
+  pdfjsLib.GlobalWorkerOptions.workerSrc = 'https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.worker.min.js';
+</script>
+<script src="{{ url_for('static', filename='js/annotation-viewer.js') }}?v=2"></script>
 <script>
 /**
  * Recipe Preview - Minimal Alpine.js component