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/pro/Nav.svelte

@@ -0,0 +1,109 @@
+<script>
+	import {link} from "svelte-spa-router";
+	import {bucket_writable, counts, strings, urls} from "../js/stores";
+	import {licence, offloadRemainingWithCount, running, tools} from "./stores";
+	import Nav from "../components/Nav.svelte";
+	import OffloadStatus from "../components/OffloadStatus.svelte";
+	import ToolRunningStatus from "./ToolRunningStatus.svelte";
+	import OffloadStatusFlyout from "../components/OffloadStatusFlyout.svelte";
+	import PanelRow from "../components/PanelRow.svelte";
+	import Button from "../components/Button.svelte";
+
+	let flyoutButton;
+	let expanded = false;
+	let hasFocus = false;
+
+	/**
+	 * Get a message describing why the offload remaining button is disabled, if it is.
+	 *
+	 * @param {Object} licence
+	 * @param {Object} counts
+	 *
+	 * @return {string}
+	 */
+	function getOffloadRemainingDisabledMessage( licence, counts ) {
+		if ( !licence.is_set ) {
+			return $strings.no_licence;
+		}
+
+		if ( counts.total < 1 ) {
+			return $strings.no_media;
+		}
+
+		if ( counts.not_offloaded < 1 ) {
+			return $strings.all_media_offloaded;
+		}
+
+		if (
+			licence.limit_info.counts_toward_limit &&
+			licence.limit_info.total > 0 &&
+			licence.limit_info.limit > 0 &&
+			licence.limit_info.total >= licence.limit_info.limit
+		) {
+			if ( licence.limit_info.total > licence.limit_info.limit ) {
+				return $strings.licence_limit_exceeded;
+			}
+
+			return $strings.licence_limit_reached;
+		}
+
+		if ( ! $bucket_writable ) {
+			return $strings.disabled_tool_bucket_access;
+		}
+
+		return "";
+	}
+
+	$: offloadRemainingDisabledMessage = getOffloadRemainingDisabledMessage( $licence, $counts );
+
+	/**
+	 * Close the flyout panel and kick off the offloader.
+	 *
+	 * The panel is closed so that it does not pop back open without focus on completion.
+	 */
+	function startOffload() {
+		expanded = false;
+		tools.start( $tools.uploader );
+	}
+</script>
+
+<Nav>
+	{#if !!$running}
+		<ToolRunningStatus/>
+	{:else}
+		<OffloadStatus bind:flyoutButton bind:expanded bind:hasFocus>
+			<svelte:fragment slot="flyout">
+				<OffloadStatusFlyout bind:expanded bind:hasFocus bind:buttonRef={flyoutButton}>
+					<svelte:fragment slot="footer">
+						<PanelRow footer class="offload-remaining">
+							<Button
+								primary
+								disabled={offloadRemainingDisabledMessage}
+								title={offloadRemainingDisabledMessage}
+								on:click={startOffload}
+							>
+								{$offloadRemainingWithCount}
+							</Button>
+						</PanelRow>
+
+						<PanelRow footer class="licence">
+							<div class="details">
+								<p class="title">{$strings.plan_usage_title}</p>
+								<p>{$licence.plan_usage}</p>
+							</div>
+							{#if !$licence.is_set}
+								<a href="/license" use:link>
+									{$strings.activate_licence}
+								</a>
+							{:else if $licence.limit_info.limit !== 0}
+								<a href={$urls.licenses} target="_blank" class="upgrade">
+									{$strings.upgrade_plan_cta}
+								</a>
+							{/if}
+						</PanelRow>
+					</svelte:fragment>
+				</OffloadStatusFlyout>
+			</svelte:fragment>
+		</OffloadStatus>
+	{/if}
+</Nav>