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

assets/css/attachment.css

@@ -0,0 +1,59 @@
+#s3-actions.postbox .inside {
+  margin: 0;
+  padding: 0;
+}
+#s3-actions.postbox a, #s3-actions.postbox a:hover {
+  text-decoration: none;
+}
+#s3-actions.postbox .s3-details {
+  padding: 6px 0;
+}
+#s3-actions.postbox .s3-details .misc-pub-section {
+  clear: both;
+  -webkit-box-sizing: border-box;
+  -moz-box-sizing: border-box;
+  box-sizing: border-box;
+}
+#s3-actions.postbox .s3-details .misc-pub-section .s3-key {
+  display: inline-block;
+  white-space: nowrap;
+}
+#s3-actions.postbox .s3-details .misc-pub-section .s3-value {
+  display: inline-block;
+  font-weight: bold;
+}
+#s3-actions.postbox .s3-details .misc-pub-section .s3-value .more-info {
+  font-weight: lighter;
+}
+#s3-actions.postbox .s3-details .misc-pub-section input.error {
+  color: #a00;
+}
+#s3-actions.postbox .s3-details .not-copied {
+  color: #666;
+}
+#s3-actions.postbox .s3-actions {
+  padding: 10px;
+  clear: both;
+  border-top: 1px solid #ddd;
+  border-bottom: 1px solid #ddd;
+  background: #f5f5f5;
+}
+#s3-actions.postbox .s3-actions .copy-action {
+  text-align: right;
+  float: right;
+  line-height: 23px;
+}
+#s3-actions.postbox .s3-actions .remove-action {
+  line-height: 28px;
+  vertical-align: middle;
+  text-align: left;
+  float: left;
+}
+#s3-actions.postbox .s3-actions .remove-action a.local-warning {
+  color: #a00;
+}
+#s3-actions.postbox .s3-actions .remove-action a.local-warning:hover {
+  color: #f00;
+}
+
+/*# sourceMappingURL=attachment.css.map */