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/DebitorDetailServiceTest.php

@@ -537,7 +537,6 @@ class DebitorDetailServiceTest extends TestCase
 
         $result = DebitorDetailService::buildSupportDashboard($tickets, 48);
 
-        $this->assertTrue($result['ok']);
         $this->assertSame(4, $result['health']['total_tickets']);
         $this->assertSame(3, $result['health']['open_tickets']);
         $this->assertSame(1, $result['health']['critical_tickets']);
@@ -566,7 +565,6 @@ class DebitorDetailServiceTest extends TestCase
 
         $result = DebitorDetailService::buildSupportDashboard($tickets, 48);
 
-        $this->assertTrue($result['ok']);
         $this->assertSame(0, $result['health']['open_tickets']);
         $this->assertSame(0, $result['health']['critical_tickets']);
         $this->assertNull($result['health']['oldest_open_age_hours']);
@@ -639,7 +637,6 @@ class DebitorDetailServiceTest extends TestCase
             'definitions_count' => 15,
         ]);
 
-        $this->assertTrue($result['ok']);
         $this->assertSame(4, $result['health']['escalation_count']);
         $this->assertTrue($result['health']['escalation_available']);
         $this->assertSame(6, $result['meta']['escalation_tickets_considered']);