Implement Settings > Media's "Allow SVG uploads" toggle (v2.3.0)

The toggle existed in the UI with no implementation behind it, so
uploads were rejected regardless of the setting. New SvgUploads class:
- Allowlists the SVG mime type and fixes WP's real-mime sniff, which
  otherwise nulls out the file type for SVGs specifically even after
  the mime allowlist is updated.
- Populates width/height metadata (parsed from the SVG's own
  viewBox/width/height) — without this, wp_get_missing_image_subsizes()
  throws undefined-array-key warnings that can corrupt the upload
  response's JSON on environments with warnings displayed inline.
- Basic sanitization on upload (strips <script> tags, inline event
  handlers, javascript: URIs).

Verified live via the REST media endpoint: clean upload with correct
dimensions, and a malicious test SVG had its script/handlers stripped
while staying valid markup.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

app/package.json

@@ -1,6 +1,6 @@
 {
   "name": "aurora-admin-app",
-  "version": "2.2.0",
+  "version": "2.3.0",
   "private": true,
   "type": "module",
   "scripts": {