Increase Playground runtime PHP memory_limit to 512M (#3936)

## Related issues

- Related to #3766
- Related to STU-1821

This PR addresses "Problem 2 (fatal errors / memory exhaustion)" from
that report.

## How AI was used in this PR

Used Claude Code to reproduce the wp-admin OOM locally, trace it to the
Playground runtime's memory cap, and verify the fix against a heavy
plugin stack.

## Proposed Changes

The reported issue is that when a site with numerous plugins is cloned
into Studio, and then run with the Playground runtime, the front-end
loads but wp-admin dies with `Fatal error: Allowed memory size of
268435456 bytes exhausted` (256 MB).

The PHP-WASM HTTP server serves every request with a hard-coded PHP
`memory_limit` of 256 MB. A realistic production plugin stack
(WooCommerce, WooPayments, Jetpack, Jetpack Boost, Jetpack CRM,
MailPoet, Site Kit, etc.) already peaks at ~224 MB on an empty database,
so wp-admin tips over 256 MB when the site's plugins and data load.

This PR raises the Playground serving `memory_limit` to 512 MB, matching
the native runtime, so the two behave consistently, and heavier sites
can open wp-admin.

| trunk | this branch |
|--------|--------|
| <img width="2358" height="2860" alt="CleanShot 2026-06-23 at 17 02
48@2x"
src="https://github.com/user-attachments/assets/ba30257a-59c1-4218-9328-221f75a426a9"
/> | <img width="2270" height="2772" alt="CleanShot 2026-06-23 at 16 59
14@2x"
src="https://github.com/user-attachments/assets/cd1d36ef-00ea-4725-8214-337c42365224"
/> |

## Testing Instructions

- Visual review should be enough

## Pre-merge Checklist

- [x] Have you checked for TypeScript, React or other console errors?
(`npm run typecheck` passes; eslint clean on the changed file.)

Author: gcsecsey

apps/cli/playground-server-child.ts

@@ -469,6 +469,7 @@ const startServer = wrapWithStartingPromise(
 			await setPhpIniEntries( server.playground, {
 				'openssl.cafile': '/internal/shared/ca-bundle.crt',
 				'curl.cainfo': '/internal/shared/ca-bundle.crt',
+				memory_limit: '512M',
 			} );
 
 			stopSignal.throwIfAborted();