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/RadioButton.svelte

@@ -0,0 +1,20 @@
+<script>
+	export let list = false;
+	export let disabled = false;
+	export let name = "options";
+	export let value = "";
+	export let selected = "";
+	export let desc = "";
+</script>
+
+<div class="radio-btn" class:list class:disabled>
+	<label>
+		<input type="radio" {name} bind:group={selected} {value} {disabled}>
+		<slot/>
+	</label>
+</div>
+{#if selected === value && desc}
+	<p class="radio-desc">
+		{@html desc}
+	</p>
+{/if}