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/DeliverySettingsPanel.svelte

@@ -0,0 +1,99 @@
+<script>
+	import {delivery_provider, settings, strings} from "../js/stores";
+	import Panel from "./Panel.svelte";
+	import DeliverySettingsHeadingRow
+		from "./DeliverySettingsHeadingRow.svelte";
+	import SettingsValidationStatusRow from "./SettingsValidationStatusRow.svelte";
+	import SettingsPanelOption from "./SettingsPanelOption.svelte";
+
+	/**
+	 * Potentially returns a reason that the provided domain name is invalid.
+	 *
+	 * @param {string} domain
+	 *
+	 * @return {string}
+	 */
+	function domainValidator( domain ) {
+		const domainPattern = /[^a-z0-9.-]/;
+
+		let message = "";
+
+		if ( domain.trim().length === 0 ) {
+			message = $strings.domain_blank;
+		} else if ( true === domainPattern.test( domain ) ) {
+			message = $strings.domain_invalid_content;
+		} else if ( domain.length < 3 ) {
+			message = $strings.domain_too_short;
+		}
+
+		return message;
+	}
+</script>
+
+<Panel name="settings" heading={$strings.delivery_settings_title} helpKey="delivery-provider">
+	<DeliverySettingsHeadingRow/>
+	<SettingsValidationStatusRow section="delivery"/>
+	<SettingsPanelOption
+		heading={$strings.rewrite_media_urls}
+		description={$delivery_provider.rewrite_media_urls_desc}
+		toggleName="serve-from-s3"
+		bind:toggle={$settings["serve-from-s3"]}
+	/>
+
+	{#if $delivery_provider.delivery_domain_allowed}
+		<SettingsPanelOption
+			heading={$strings.delivery_domain}
+			description={$delivery_provider.delivery_domain_desc}
+			toggleName="enable-delivery-domain"
+			bind:toggle={$settings["enable-delivery-domain"]}
+			textName="delivery-domain"
+			bind:text={$settings["delivery-domain"]}
+			validator={domainValidator}
+		/>
+		{#if $delivery_provider.use_signed_urls_key_file_allowed && $settings[ "enable-delivery-domain" ]}
+			<SettingsPanelOption
+				heading={$delivery_provider.signed_urls_option_name}
+				description={$delivery_provider.signed_urls_option_description}
+				toggleName="enable-signed-urls"
+				bind:toggle={$settings["enable-signed-urls"]}
+			>
+				<!-- Currently only CloudFront needs a key file for signing -->
+				{#if $settings[ "enable-signed-urls" ]}
+					<SettingsPanelOption
+						heading={$delivery_provider.signed_urls_key_id_name}
+						description={$delivery_provider.signed_urls_key_id_description}
+						textName="signed-urls-key-id"
+						bind:text={$settings["signed-urls-key-id"]}
+						nested={true}
+						first={true}
+					/>
+
+					<SettingsPanelOption
+						heading={$delivery_provider.signed_urls_key_file_path_name}
+						description={$delivery_provider.signed_urls_key_file_path_description}
+						textName="signed-urls-key-file-path"
+						bind:text={$settings["signed-urls-key-file-path"]}
+						placeholder={$delivery_provider.signed_urls_key_file_path_placeholder}
+						nested={true}
+					/>
+
+					<SettingsPanelOption
+						heading={$delivery_provider.signed_urls_object_prefix_name}
+						description={$delivery_provider.signed_urls_object_prefix_description}
+						textName="signed-urls-object-prefix"
+						bind:text={$settings["signed-urls-object-prefix"]}
+						placeholder="private/"
+						nested={true}
+					/>
+				{/if}
+			</SettingsPanelOption>
+		{/if}
+	{/if}
+
+	<SettingsPanelOption
+		heading={$strings.force_https}
+		description={$strings.force_https_desc}
+		toggleName="force-https"
+		bind:toggle={$settings["force-https"]}
+	/>
+</Panel>