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/TabButton.svelte

@@ -0,0 +1,37 @@
+<script>
+	import {strings, urls} from "../js/stores";
+
+	export let active = false;
+	export let disabled = false;
+	export let icon = "";
+	export let iconDesc = "";
+	export let text = ""
+	export let url = $urls.settings;
+</script>
+
+<a
+	href={url}
+	class="button-tab"
+	class:active
+	class:btn-disabled={disabled}
+	{disabled}
+	on:click|preventDefault
+>
+	{#if icon}
+		<img
+			src={icon}
+			type="image/svg+xml"
+			alt={iconDesc}
+		>
+	{/if}
+	{#if text}
+		<p>{text}</p>
+	{/if}
+	{#if active}
+		<img
+			class="checkmark"
+			src="{$urls.assets + 'img/icon/licence-checked.svg'}"
+			type="image/svg+xml" alt={$strings.selected_desc}
+		>
+	{/if}
+</a>