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

vendor/Gcp/google/grpc-gcp/cloudprober/cloudprober.cfg

@@ -0,0 +1,31 @@
+probe {
+  type: EXTERNAL
+  name: "spanner"
+  interval_msec: 1800000
+  timeout_msec: 30000
+  targets { dummy_targets {} }  # No targets for external probe
+  external_probe {
+    mode: ONCE
+    command: "php grpc_gpc_prober/prober.php --api=spanner"
+  }
+}
+
+probe {
+  type: EXTERNAL
+  name: "firestore"
+  interval_msec: 1800000
+  timeout_msec: 30000
+  targets { dummy_targets {} }  # No targets for external probe
+  external_probe {
+    mode: ONCE
+    command: "php grpc_gpc_prober/prober.php --api=firestore"
+  }
+}
+
+surfacer {
+  type: STACKDRIVER
+  name: "stackdriver"
+  stackdriver_surfacer {
+    monitoring_url: "custom.googleapis.com/cloudprober/"
+  }
+}