feat(sidecars): surface storage location and cover excluded models in migration

After migrating to centralized sidecar storage users had no indication
where their files went, and portable-mode installs silently placed the
sidecar root inside the plugin folder where a reinstall or git clean
would delete it.

- Migration now also covers models excluded from the library view and
  returns the resolved sidecar root in its result payload
- get_settings exposes the resolved sidecar root, whether it is the
  default, and whether it lives inside the installation folder
- New POST /api/lm/sidecars/open-location endpoint opens (or copies)
  the sidecar storage folder
- Settings UI always shows the effective storage path with an
  open-folder button, and warns when the root is inside the
  installation folder (portable-mode hazard)
- Migration confirmation shows the destination; on completion a result
  dialog summarizes moved/skipped/conflict counts with the storage
  location and an open-folder action
- Ignore /sidecars/ at the repository root so portable-mode sidecars
  are never committed

Refs #1045

templates/components/modals/confirm_modals.html

@@ -103,6 +103,7 @@
     <div class="modal-content delete-modal-content">
         <h2 data-role="title"></h2>
         <p class="delete-message" data-role="message"></p>
+        <p class="delete-message sidecar-migration-destination" data-role="destination" style="display: none;"></p>
         <div class="modal-actions">
             <button class="cancel-btn" data-action="cancel-sidecar-migration">{{ t('common.actions.cancel') }}</button>
             <button class="primary-btn" data-action="confirm-sidecar-migration"></button>
@@ -110,6 +111,22 @@
     </div>
 </div>
 
+<!-- Sidecar Migration Result Modal
+     Self-managed by SettingsManager: shown after a migration run with the
+     outcome counters and the storage location; closing it reloads the page
+     so cards pick up the new paths. -->
+<div id="sidecarMigrationResultModal" class="modal delete-modal">
+    <div class="modal-content delete-modal-content">
+        <h2 data-role="title"></h2>
+        <p class="delete-message" data-role="message"></p>
+        <p class="delete-message sidecar-migration-destination" data-role="destination" style="display: none;"></p>
+        <div class="modal-actions">
+            <button class="secondary-btn" data-action="open-sidecar-location" style="display: none;">{{ t('settings.sidecarStorage.openFolderButton') }}</button>
+            <button class="primary-btn" data-action="close-sidecar-result">{{ t('common.actions.close') }}</button>
+        </div>
+    </div>
+</div>
+
 <!-- Sidebar Folder Delete Confirmation Modal -->
 <!-- Shared by two states: 'confirm' (model-free folder) and 'blocked' (the
      subtree still holds models, so a cascade delete is refused). -->

templates/components/modals/settings/library.html

@@ -359,6 +359,23 @@
                     </div>
                 </div>
             </div>
+            <div class="setting-row">
+                <div class="setting-info">
+                    <div class="input-help sidecar-storage-location">
+                        {{ t('settings.sidecarStorage.effectivePathLabel') }}
+                        <code id="sidecarStorageResolvedPath" class="backup-location-path"></code>
+                    </div>
+                    <div class="input-help sidecar-storage-repo-warning" id="sidecarStorageRepoWarning" style="display: none;">
+                        <i class="fas fa-exclamation-triangle"></i>
+                        {{ t('settings.sidecarStorage.repoWarning') }}
+                    </div>
+                </div>
+                <div class="setting-control">
+                    <button type="button" class="secondary-btn" id="sidecarStorageOpenBtn" onclick="settingsManager.openSidecarStorageLocation()">
+                        {{ t('settings.sidecarStorage.openFolderButton') }}
+                    </button>
+                </div>
+            </div>
         </div>
 
         <div class="setting-item">