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/helpers/ui.php

@@ -146,9 +146,6 @@ function selectFilter(
 function renderGridFilterToolbar(array $schema, array $active = [], array $optionSets = []): void
 {
     foreach ($schema as $field) {
-        if (!is_array($field)) {
-            continue;
-        }
         if (($field['render'] ?? true) === false) {
             continue;
         }
@@ -463,10 +460,10 @@ function appStylePathsForGroups(array $groupNames): array
         $registry = app(\MintyPHP\App\Module\ModuleRegistry::class);
         if ($registry instanceof \MintyPHP\App\Module\ModuleRegistry) {
             foreach ($registry->getAssetGroups() as $groupName => $paths) {
-                if (!is_string($groupName) || $groupName === '') {
+                if ($groupName === '') {
                     continue;
                 }
-                if (!is_array($paths) || isset($groups[$groupName])) {
+                if (isset($groups[$groupName])) {
                     continue;
                 }
                 $groups[$groupName] = $paths;