Fix plugin security, hooks system, and admin features

- Add plugin allowlist (enabled_plugins in config.json)
- Add enable/disable toggle in admin (separate from visibility)
- Add plugin hooks system (actions + filters with auto-registration)
- Fix autoLinkPageTitles nested <a> tag vulnerability
- Move MQTT credentials to environment variables
- Preserve current page in language switcher
- Fix ctime/birthtime for file creation date
- Deduplicate getGuidePage() CommonMark setup
- Simplify formatDisplayName() logic
- Add admin activity log to dashboard
- Add own password change with current password verification
- Apply theme header_color to admin sidebar
- Add content preview button in editor

config.json

@@ -20,6 +20,11 @@
         "website": "https:\/\/noorlander.info"
     },
     "show_version": false,
+    "enabled_plugins": [
+        "MQTTTracker",
+        "HTMLBlock",
+        "test"
+    ],
     "features": {
         "auto_link_pages": true,
         "search_enabled": true,