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

ui/components/ToolsUpgrade.svelte

@@ -0,0 +1,38 @@
+<script>
+	import {strings, urls} from "../js/stores";
+	import Upsell from "./Upsell.svelte";
+
+	let benefits = [
+		{
+			icon: $urls.assets + 'img/icon/offload-remaining.svg',
+			alt: 'offload icon',
+			text: $strings.tools_uppsell_benefits.offload,
+		},
+		{
+			icon: $urls.assets + 'img/icon/download.svg',
+			alt: 'download icon',
+			text: $strings.tools_uppsell_benefits.download,
+		},
+		{
+			icon: $urls.assets + 'img/icon/remove-from-bucket.svg',
+			alt: 'remove from bucket icon',
+			text: $strings.tools_uppsell_benefits.remove_bucket,
+		},
+		{
+			icon: $urls.assets + 'img/icon/remove-from-server.svg',
+			alt: 'remove from server icon',
+			text: $strings.tools_uppsell_benefits.remove_server,
+		},
+	];
+</script>
+
+<Upsell benefits={benefits}>
+	<div slot="heading">{$strings.tools_upsell_heading}</div>
+
+	<div slot="description">{@html $strings.tools_upsell_description}</div>
+
+	<a slot="call-to-action" href={$urls.upsell_discount_tools} class="button btn-lg btn-primary">
+		<img src={$urls.assets + "img/icon/stars.svg"} alt="stars icon" style="margin-right: 5px;">
+		{$strings.tools_upsell_cta}
+	</a>
+</Upsell>