[5.x] replace 404 and 406 CRITICAL errors with NOTICE and useful information

[MarcelSchuermann]

Pull Request for Issue #45781

Summary of Changes

404 and 406 exceptions should be handled correctly with useful information and as NOTICE instead of unspecific CRITICAL Error, so the log is not overloaded and unspecific.

Testing Instructions

1. Set up a standard Joomla 5.x installation.
2. In Global Configuration -> Logging, enable logging to capture errors.
3. Navigate to any URL on the frontend that does not exist f.e.:
   yourpage/asdf
4. Check logs in joomlaroot/administrator/logs
5. See critical unspecific error

Actual result BEFORE applying this Pull Request

A log entry with 404 or 406 exceptions end up in CRITICAL unspecific / unhandled ERROR log.

2025-07-25T15:17:44+00:00	CRITICAL ::1	error	Uncaught Throwable of type Joomla\CMS\Router\Exception\RouteNotFoundException thrown with message "Seite nicht gefunden". Stack trace: #0 [ROOT]\libraries\src\Application\SiteApplication.php(767): Joomla\CMS\Router\Router->parse(Object(Joomla\CMS\Uri\Uri), true)
#1 [ROOT]\libraries\src\Application\SiteApplication.php(243): Joomla\CMS\Application\SiteApplication->route()
#2 [ROOT]\libraries\src\Application\CMSApplication.php(304): Joomla\CMS\Application\SiteApplication->doExecute()
#3 [ROOT]\includes\app.php(58): Joomla\CMS\Application\CMSApplication->execute()
#4 [ROOT]\index.php(32): require_once('C:\\Web\\xampp\\ht...')
#5 {main}

Expected result AFTER applying this Pull Request

A log entry with a handled NOTICE message including f.e. the page, which was accessed.

2025-10-15T19:43:30+00:00 NOTICE ::1 client-error Page not found (404): http://localhost:8080/yourwebsite/asdfs. Message: "Seite nicht gefunden"

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed