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/grid.php

@@ -206,9 +206,6 @@ function gridSplitToolbarSchema(array $toolbarSchema, array $searchKeys = []): a
     $search = [];
     $drawer = [];
     foreach ($toolbarSchema as $field) {
-        if (!is_array($field)) {
-            continue;
-        }
         $key = trim((string) ($field['key'] ?? ''));
         $isSearch = (bool) ($field['search'] ?? false) || ($key !== '' && isset($searchKeyMap[$key]));
         if ($isSearch) {
@@ -231,9 +228,6 @@ function gridSchemaByKey(array $toolbarSchema): array
 {
     $schemaByKey = [];
     foreach ($toolbarSchema as $field) {
-        if (!is_array($field)) {
-            continue;
-        }
         $key = trim((string) ($field['key'] ?? ''));
         if ($key === '') {
             continue;
@@ -255,9 +249,6 @@ function gridBuildToolbarFilterState(array $toolbarSchema, array $filterState):
 {
     $state = [];
     foreach ($toolbarSchema as $field) {
-        if (!is_array($field)) {
-            continue;
-        }
 
         $key = trim((string) ($field['key'] ?? ''));
         if ($key === '') {
@@ -347,9 +338,6 @@ function gridOptionMapFromItems(array $items): array
 {
     $map = [];
     foreach ($items as $item) {
-        if (!is_array($item)) {
-            continue;
-        }
         $id = trim((string) ($item['id'] ?? ''));
         if ($id === '') {
             continue;
@@ -370,9 +358,6 @@ function gridOptionMapFromAllowed(array $field): array
 {
     $map = [];
     foreach ((array) ($field['allowed'] ?? []) as $item) {
-        if (!is_array($item)) {
-            continue;
-        }
         $id = trim((string) ($item['id'] ?? ''));
         if ($id === '') {
             continue;