Address PR review: rename to eda_visibility, merge migrations, API versioning

Changes based on jbtronics' review of PR #1241:

- Rename kicad_export -> eda_visibility (entities, forms, templates,
  translations, tests) with nullable bool for system default support
- Merge two database migrations into one (Version20260211000000)
- Rename createCachedJsonResponse -> createCacheableJsonResponse
- Change bool $apiV2 -> int $apiVersion with version validation
- EDA visibility field only shown for part parameters, not other entities
- PopulateKicadCommand: check alternative names of footprints/categories
- PopulateKicadCommand: support external JSON mapping file (--mapping-file)
- Ship default mappings JSON at contrib/kicad-populate/default_mappings.json
- Add system-wide defaultEdaVisibility setting in KiCadEDASettings
- Add KiCad HTTP Library v2 spec link in controller docs

templates/parts/edit/_specifications.html.twig

@@ -14,7 +14,7 @@
             <th>{% trans %}specifications.unit{% endtrans %}</th>
             <th>{% trans %}specifications.text{% endtrans %}</th>
             <th>{% trans %}specifications.group{% endtrans %}</th>
-            <th title="{% trans %}specifications.kicad_export.help{% endtrans %}"><i class="fas fa-bolt fa-fw"></i></th>
+            <th title="{% trans %}specifications.eda_visibility.help{% endtrans %}"><i class="fas fa-bolt fa-fw"></i></th>
             <th></th>
         </tr>
         </thead>