feat(my-videos): bucket object listing for reconciliation (Phase 2, step 2)

Adds the bucket-enumeration primitive the My Videos tab needs to find orphan and
missing files:
- s3 layer: ListObjectsV2Command wired into the SDK wrapper + a paginated
  listObjects({ s3, bucket, prefix, maxKeys }) helper (follows continuation
  tokens, bounded by maxKeys).
- r2Service.listVideoStorageObjects({ npub|pubkey }) — unlock-gated, lists under
  the user's own u/<npub>/ prefix; returns { ok, reason, keys }. Body lives in
  r2ServiceHelpers (with a shared buildProviderClient) so r2Service stays under
  its file-size budget; ensureS3SdkLoaded is injectable via ctx for testing.

Tests + mutation-verified: never lists while locked (storage-locked, no call),
no-connection / missing-bucket gating, and unlocked listing is scoped to the
user's own u/<npub>/ prefix (empty-prefix mutation fails). Removing the lock gate
or widening the prefix each fail a scenario.

Build + full lint green (r2Service back under limit).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

js/services/r2Service.js

@@ -35,6 +35,7 @@ import {
   ensureBucketCors,
   ensureBucketExists,
   deleteObject,
+  listObjects,
 } from "../storage/s3-multipart.js";
 import { ensureS3SdkLoaded, makeS3Client } from "../storage/s3-client.js";
 import { truncateMiddle } from "../utils/formatters.js";
@@ -60,6 +61,7 @@ import {
   createDefaultSettings,
   safeDecodeNpub,
   verifyPublicAccess as verifyPublicAccessHelper,
+  listVideoStorageObjects as listVideoStorageObjectsHelper,
 } from "./r2ServiceHelpers.js";
 
 const STATUS_VARIANTS = new Set(["info", "success", "error", "warning"]);
@@ -76,6 +78,7 @@ export class R2Service {
     ensureBucketExists: ensureBucketExistsOverride,
     ensureBucketCors: ensureBucketCorsOverride,
     deleteObject: deleteObjectOverride,
+    listObjects: listObjectsOverride,
   } = {}) {
     this.listeners = new Map();
     this.cloudflareSettings = null;
@@ -85,6 +88,7 @@ export class R2Service {
     this.ensureBucketExists = ensureBucketExistsOverride || ensureBucketExists;
     this.ensureBucketCors = ensureBucketCorsOverride || ensureBucketCors;
     this.deleteObject = deleteObjectOverride || deleteObject;
+    this.listObjects = listObjectsOverride || listObjects;
   }
 
   /**
@@ -226,6 +230,15 @@ export class R2Service {
     return summary;
   }
 
+  /**
+   * List the object keys under the user's storage prefix (u/<npub>/) so the
+   * "My Videos" tab can reconcile notes against actual bucket contents. Unlock-
+   * gated (needs credentials); returns { ok, reason, keys }.
+   */
+  async listVideoStorageObjects(args = {}) {
+    return listVideoStorageObjectsHelper(this, args);
+  }
+
   on(event, handler) {
     if (typeof handler !== "function") {
       return () => {};