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/audit/lib/Module/Audit/Repository/UserLifecycleAuditRepository.php

@@ -65,17 +65,17 @@ class UserLifecycleAuditRepository
         $actions = RepoQuery::normalizeStringList(
             $filters['actions'] ?? '',
             self::FILTER_OPTIONS_LIMIT_MAX,
-            static fn (string $value): string => UserLifecycleAction::tryNormalize($value)?->value ?? ''
+            static fn (string $value): string => UserLifecycleAction::tryNormalize($value)->value ?? ''
         );
         $statuses = RepoQuery::normalizeStringList(
             $filters['statuses'] ?? '',
             self::FILTER_OPTIONS_LIMIT_MAX,
-            static fn (string $value): string => UserLifecycleStatus::tryNormalize($value)?->value ?? ''
+            static fn (string $value): string => UserLifecycleStatus::tryNormalize($value)->value ?? ''
         );
         $triggerTypes = RepoQuery::normalizeStringList(
             $filters['trigger_types'] ?? '',
             self::FILTER_OPTIONS_LIMIT_MAX,
-            static fn (string $value): string => UserLifecycleTriggerType::tryNormalize($value)?->value ?? ''
+            static fn (string $value): string => UserLifecycleTriggerType::tryNormalize($value)->value ?? ''
         );
         $actorUserIds = array_slice(
             RepoQuery::normalizeIdList($filters['actor_user_ids'] ?? ''),