refactor: remove dead code via Rector

rector.php gets the deadCode set: @param/@return/@var tags that only
repeat native types, === true comparisons, three unused constructor
dependencies (DateService, ProductDataService, AjaxWatchlistController),
the unused reseller lookup in ContextProcessor and an always-false check
in AbstractMappedFinisher (trimExplode with removeEmpty never yields an
empty remote name).

Checked locally: 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

@@ -28,6 +28,7 @@ return RectorConfig::configure()
     ])
     ->withPhpVersion(PhpVersion::PHP_85)
     ->withPhpSets(php85: true)
+    ->withPreparedSets(deadCode: true)
     ->withSets([
         Typo3SetList::GENERAL,
         Typo3LevelSetList::UP_TO_TYPO3_13,