refactor: fix all 105 PHPStan 2 strict type findings across core and modules

Resolve all non-false-positive PHPStan 2 findings, reducing the baseline
from 486 to 382 entries (only unused-public false positives remain).

Categories fixed:
- Remove 39 redundant type checks (is_string, is_array, is_object, method_exists)
- Remove 12 no-op array_values() on already-sequential lists
- Simplify 13 null-coalesce on guaranteed offsets
- Remove 8 always-true instanceof checks
- Replace 12 redundant test assertions (assertTrue(true) → addToAssertionCount)
- Simplify 6 unnecessary nullsafe operators (?-> → ->)
- Fix 6 always-true !== '' comparisons
- Fix remaining: unset.offset, return.unusedType, staticMethod narrowing

53 files changed across core/, modules/, pages/, and tests/.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

modules/helpdesk/tests/Module/Helpdesk/Service/TicketCommunicationServiceTest.php

@@ -36,8 +36,7 @@ class TicketCommunicationServiceTest extends TestCase
         $service = new TicketCommunicationService($soapGateway, $odataGateway);
         $result = $service->loadTicketCommunicationFeed('T26-1216', 40);
 
-        $this->assertTrue($result['ok']);
-        $this->assertIsArray($result['entries']);
+        $this->assertNotEmpty($result['entries']);
         $this->assertGreaterThanOrEqual(3, count($result['entries']));
         $this->assertSame(true, $result['meta']['soap_used']);
         $this->assertSame(false, $result['meta']['fallback_used']);