Add Oribi Sync plugin for syncing WordPress pages and theme files from a Git repository

- Implement encryption helpers for storing and retrieving the Personal Access Token (PAT).
- Create REST API endpoints for triggering sync, checking sync status, and handling webhooks.
- Develop the sync engine to fetch pages from the Git repository, create/update WordPress pages, and trash removed pages.
- Add functionality for previewing and applying theme files from the repository.
- Set up plugin activation and deactivation hooks to manage default options and scheduled tasks.
- Implement uninstall routine to clean up plugin options and metadata from posts.

assets/admin.css

@@ -0,0 +1,37 @@
+/**
+ * Oribi Sync — Admin styles
+ */
+
+.oribi-sync-wrap .form-table th {
+    width: 200px;
+}
+
+.oribi-sync-wrap .button {
+    margin-right: 6px;
+}
+
+.oribi-sync-wrap hr {
+    margin: 24px 0;
+    border: none;
+    border-top: 1px solid #ddd;
+}
+
+.oribi-sync-log td,
+.oribi-sync-log th {
+    font-size: 13px;
+    padding: 6px 8px;
+}
+
+.oribi-sync-wrap details summary {
+    cursor: pointer;
+    color: #2271b1;
+    font-size: 13px;
+}
+
+.oribi-sync-wrap details summary:hover {
+    text-decoration: underline;
+}
+
+.oribi-sync-wrap .description code {
+    font-size: 12px;
+}