refactor: code quality via Rector, strict types where safe

rector.php gets the codeQuality set: declare(strict_types=1) in the 85
files where Rector finds no call relying on scalar type juggling (mostly
TCA and configuration, models, the content feed API and the import
command), "or die" as "|| die", instanceof instead of null checks for
object types, early returns and self:: in final classes.

Hotel::setRooms() goes instead of getting the property Rector wanted to
declare: nothing calls it, and there is no rooms column any more.

Checked locally: cache warmup, the ep:* commands load, frontend crawl
(~1,900 URLs) and the backchannel APIs render the same as before.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

rector.php

@@ -28,7 +28,7 @@ return RectorConfig::configure()
     ])
     ->withPhpVersion(PhpVersion::PHP_85)
     ->withPhpSets(php85: true)
-    ->withPreparedSets(deadCode: true)
+    ->withPreparedSets(deadCode: true, codeQuality: true)
     ->withSets([
         Typo3SetList::GENERAL,
         Typo3LevelSetList::UP_TO_TYPO3_13,