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/Button.svelte

@@ -0,0 +1,76 @@
+<script>
+	import {createEventDispatcher} from "svelte";
+
+	import {urls} from "../js/stores";
+
+	const classes = $$props.class ? $$props.class : "";
+	const dispatch = createEventDispatcher();
+
+	export let ref = {};
+
+	// Button sizes, medium is the default.
+	export let extraSmall = false;
+	export let small = false;
+	export let large = false;
+	export let medium = !extraSmall && !small && !large;
+
+	// Button styles, outline is the default.
+	export let primary = false;
+	export let expandable = false;
+	export let refresh = false;
+	export let outline = !primary && !expandable && !refresh;
+
+	// Is the button disabled? Defaults to false.
+	export let disabled = false;
+
+	// Is the button in an expanded state? Defaults to false.
+	export let expanded = false;
+
+	// Is the button in a refreshing state? Defaults to false.
+	export let refreshing = false;
+
+	// A button can have a title, most useful to give a reason when disabled.
+	export let title = "";
+
+	/**
+	 * Catch escape key and emit a custom cancel event.
+	 *
+	 * @param {KeyboardEvent} event
+	 */
+	function handleKeyup( event ) {
+		if ( event.key === "Escape" ) {
+			event.preventDefault();
+			dispatch( "cancel" );
+		}
+	}
+
+	function refreshIcon( refreshing ) {
+		return $urls.assets + 'img/icon/' + (refreshing ? 'refresh-disabled.svg' : 'refresh.svg');
+	}
+</script>
+
+<button
+	on:click|preventDefault
+	class:btn-xs={extraSmall}
+	class:btn-sm={small}
+	class:btn-md={medium}
+	class:btn-lg={large}
+	class:btn-primary={primary}
+	class:btn-outline={outline}
+	class:btn-expandable={expandable}
+	class:btn-disabled={disabled}
+	class:btn-expanded={expanded}
+	class:btn-refresh={refresh}
+	class:btn-refreshing={refreshing}
+	class={classes}
+	{title}
+	disabled={disabled || refreshing}
+	bind:this={ref}
+	on:focusout
+	on:keyup={handleKeyup}
+>
+	{#if refresh}
+		<img class="icon refresh" class:refreshing src="{refreshIcon(refreshing)}" alt={title}/>
+	{/if}
+	<slot/>
+</button>