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/Service/Auth/TenantSsoService.php

@@ -278,12 +278,10 @@ class TenantSsoService
             if ($auth['client_secret_override_enc'] === '') {
                 return ['ok' => false, 'error' => 'client_secret_override_required'];
             }
-            if ($auth['client_secret_override_enc'] !== '') {
-                try {
-                    $clientSecret = $this->cryptoGateway->decryptString($auth['client_secret_override_enc']);
-                } catch (\Throwable $exception) {
-                    return ['ok' => false, 'error' => 'secret_invalid'];
-                }
+            try {
+                $clientSecret = $this->cryptoGateway->decryptString($auth['client_secret_override_enc']);
+            } catch (\Throwable $exception) {
+                return ['ok' => false, 'error' => 'secret_invalid'];
             }
             if (trim($clientSecret) === '') {
                 return ['ok' => false, 'error' => 'client_secret_override_required'];