feat: add S3-compatible storage provider (MinIO, Ceph, R2, etc.)

Adds a new 'S3-Compatible Storage' provider that works with any
S3-API-compatible object storage service, including MinIO, Ceph,
Cloudflare R2, Backblaze B2, and others.

Changes:
- New provider class: classes/providers/storage/s3-compatible-provider.php
  - Provider key: s3compatible
  - Reads user-configured endpoint URL from settings
  - Uses path-style URL access (required by most S3-compatible services)
  - Supports credentials via AS3CF_S3COMPAT_ACCESS_KEY_ID /
    AS3CF_S3COMPAT_SECRET_ACCESS_KEY wp-config.php constants
  - Disables AWS-specific features (Block Public Access, Object Ownership)
- New provider SVG icons (s3compatible.svg, -link.svg, -round.svg)
- Registered provider in main plugin class with endpoint setting support
- Updated StorageProviderSubPage to show endpoint URL input for S3-compatible
- Built pro settings bundle with rollup (Svelte 4.2.19)
- Added package.json and updated rollup.config.mjs for pro-only builds

assets/img/icon/provider/storage/aws.svg

@@ -0,0 +1,3 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24">
+  <path fill="#FA7460" d="M17.5,6 L21.5,4.5 L17.5,3 L13.5,4.5 L17.5,6 Z M18,7 L18,12 L22,10.5 L22,5.5 L18,7 Z M17,7 L13,5.5 L13,10.5 L17,12 L17,7 Z M6.5,6 L10.5,4.5 L6.5,3 L2.5,4.5 L6.5,6 Z M7,7 L7,12 L11,10.5 L11,5.5 L7,7 Z M6,7 L2,5.5 L2,10.5 L6,12 L6,7 Z M12,16 L16,14.5 L12,13 L8,14.5 L12,16 Z M12.5,17 L12.5,22 L16.5,20.5 L16.5,15.5 L12.5,17 Z M11.5,17 L7.5,15.5 L7.5,20.5 L11.5,22 L11.5,17 Z"/>
+</svg>