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>

core/Http/ApiResponse.php

@@ -243,7 +243,7 @@ class ApiResponse
         try {
             if (is_callable(self::$apiAuditServiceResolver)) {
                 $service = (self::$apiAuditServiceResolver)();
-                if (is_object($service) && method_exists($service, 'finish')) {
+                if (method_exists($service, 'finish')) {
                     $service->finish($statusCode, $errorCode);
                 }
             }
@@ -257,7 +257,7 @@ class ApiResponse
         try {
             if (is_callable(self::$apiAuditServiceResolver)) {
                 $service = (self::$apiAuditServiceResolver)();
-                if (is_object($service) && method_exists($service, 'currentRequestId')) {
+                if (method_exists($service, 'currentRequestId')) {
                     return $service->currentRequestId();
                 }
             }
@@ -273,12 +273,7 @@ class ApiResponse
             throw new \RuntimeException('ApiResponse is not configured for dependency: ' . AuthorizationService::class);
         }
 
-        $service = (self::$authorizationServiceResolver)();
-        if (!$service instanceof AuthorizationService) {
-            throw new \RuntimeException('ApiResponse resolver returned invalid dependency: ' . AuthorizationService::class);
-        }
-
-        return $service;
+        return (self::$authorizationServiceResolver)();
     }
 
     private static function finishSystemAuditReporter(int $statusCode, ?string $errorCode = null): void
@@ -286,7 +281,7 @@ class ApiResponse
         try {
             if (is_callable(self::$apiSystemAuditReporterResolver)) {
                 $service = (self::$apiSystemAuditReporterResolver)();
-                if (is_object($service) && method_exists($service, 'finish')) {
+                if (method_exists($service, 'finish')) {
                     $service->finish($statusCode, $errorCode);
                 }
             }