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/StoragePage.svelte

@@ -0,0 +1,52 @@
+<script>
+	import {afterUpdate, setContext} from "svelte";
+	import {location, push} from "svelte-spa-router";
+	import {
+		current_settings,
+		settingsLocked,
+		needs_access_keys
+	} from "../js/stores";
+	import Page from "./Page.svelte";
+	import Notifications from "./Notifications.svelte";
+	import SubNav from "./SubNav.svelte";
+	import SubPages from "./SubPages.svelte";
+	import {pages} from "../js/routes";
+
+	export let name = "storage";
+	export let params = {}; // Required for regex routes.
+	const _params = params; // Stops compiler warning about unused params export;
+
+	// During initial setup some storage sub pages behave differently.
+	// Not having a bucket defined is akin to initial setup, but changing provider in sub page may also flip the switch.
+	if ( $current_settings.bucket ) {
+		setContext( "initialSetup", false );
+	} else {
+		setContext( "initialSetup", true );
+	}
+
+	// Let all child components know if settings are currently locked.
+	setContext( "settingsLocked", settingsLocked );
+
+	const prefix = "/storage";
+
+	let items = pages.withPrefix( prefix );
+	let routes = pages.routes( prefix );
+
+	afterUpdate( () => {
+		items = pages.withPrefix( prefix );
+		routes = pages.routes( prefix );
+
+		// Ensure only Storage Provider subpage can be visited if credentials not set.
+		if ( $needs_access_keys && $location.startsWith( "/storage/" ) && $location !== "/storage/provider" ) {
+			push( "/storage/provider" );
+		}
+	} );
+</script>
+
+<Page {name} subpage on:routeEvent>
+	<Notifications tab="media" tabParent="media"/>
+
+	<SubNav {name} {items} progress/>
+
+	<SubPages {name} {prefix} {routes} on:routeEvent/>
+</Page>