schema: re-introspect Unraid API against 7.3

7.3 findings (all existing queries confirmed working — no breaking changes):
- ArrayParity/ArrayCache no longer exist as named types; everything is ArrayDisk
- InfoOs gained: kernel, arch, fqdn, build, codename, platform, serial, uefi
- InfoCpu gained: manufacturer, model, speed, speedmin/max, processors, socket, topology
- ArrayDisk gained: idx, numReads/Writes/Errors, warning/critical temps, color, fsType
- MemoryUtilization gained: free, active, buffcache, swapFree, percentSwapTotal

Changes:
- Add kernel to master GQL query (useful for display)
- Update schema comments to reflect 7.3 reality
- Remove ArrayParity/ArrayCache from api_test.php introspection (now null types)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Plugin/unraid/api/api_test.php

@@ -67,7 +67,8 @@ if ($key) {
 
 // ── Schema introspection — discover actual field names ────────────────────────
 if ($key) {
-    $types = ['InfoOs','InfoCpu','InfoMemory','ArrayDisk','ArrayParity','ArrayCache','Vm','Domain','VmDomain'];
+    // ArrayParity and ArrayCache were separate named types in 7.2.5 — removed in 7.3 (now same as ArrayDisk)
+    $types = ['InfoOs','InfoCpu','InfoMemory','ArrayDisk','VmDomain'];
     $introspectGql = '{ ' . implode(' ', array_map(fn($t) =>
         "{$t}: __type(name: \"{$t}\") { fields { name type { name kind ofType { name kind } } } }",
         $types