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/Support/Guard.php

@@ -145,11 +145,7 @@ class Guard
         if (!is_callable(self::$authorizationServiceResolver)) {
             throw new \RuntimeException('Guard is not configured for dependency: ' . AuthorizationService::class);
         }
-        $service = (self::$authorizationServiceResolver)();
-        if (!$service instanceof AuthorizationService) {
-            throw new \RuntimeException('Guard resolver returned invalid dependency: ' . AuthorizationService::class);
-        }
-        return $service;
+        return (self::$authorizationServiceResolver)();
     }
 
     private static function authService(): AuthService
@@ -157,11 +153,7 @@ class Guard
         if (!is_callable(self::$authServiceResolver)) {
             throw new \RuntimeException('Guard is not configured for dependency: ' . AuthService::class);
         }
-        $service = (self::$authServiceResolver)();
-        if (!$service instanceof AuthService) {
-            throw new \RuntimeException('Guard resolver returned invalid dependency: ' . AuthService::class);
-        }
-        return $service;
+        return (self::$authServiceResolver)();
     }
 
     private static function tenantService(): TenantService
@@ -169,11 +161,7 @@ class Guard
         if (!is_callable(self::$tenantServiceResolver)) {
             throw new \RuntimeException('Guard is not configured for dependency: ' . TenantService::class);
         }
-        $service = (self::$tenantServiceResolver)();
-        if (!$service instanceof TenantService) {
-            throw new \RuntimeException('Guard resolver returned invalid dependency: ' . TenantService::class);
-        }
-        return $service;
+        return (self::$tenantServiceResolver)();
     }
 
     private static function isAllowedByAbility(int $userId, string $ability, array $context = []): bool