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

rollup.config.mjs

@@ -0,0 +1,46 @@
+import svelte from 'rollup-plugin-svelte';
+import commonjs from '@rollup/plugin-commonjs';
+import resolve from '@rollup/plugin-node-resolve';
+import css from 'rollup-plugin-css-only';
+
+// const production = !process.env.ROLLUP_WATCH;
+const production = false; // Keep runtime checks for the moment.
+
+// Note: ui/lite/Settings.svelte belongs to the base plugin (not present in this Pro-only repo).
+// The base plugin's compiled output (assets/js/settings.js) is committed directly.
+// This config only builds the Pro-specific entry point.
+
+export default [{
+	input: 'ui/pro/Settings.svelte',
+	output: {
+		sourcemap: true,
+		format: 'umd',
+		name: 'AS3CFPro_Settings',
+		file: 'assets/js/pro/settings.js'
+	},
+	plugins: [
+		svelte( {
+			compilerOptions: {
+				// enable run-time checks when not in production
+				dev: !production
+			}
+		} ),
+		// we'll extract any component CSS out into
+		// a separate file - better for performance
+		css( { output: 'settings.css' } ),
+
+		// If you have external dependencies installed from
+		// npm, you'll most likely need these plugins. In
+		// some cases you'll need additional configuration -
+		// consult the documentation for details:
+		// https://github.com/rollup/plugins/tree/master/packages/commonjs
+		resolve( {
+			browser: true,
+			dedupe: ['svelte']
+		} ),
+		commonjs()
+	],
+	watch: {
+		clearScreen: false
+	}
+}];