feat(edit): thumbnail + video file upload in Edit modal (steps 2-3/3)

Brings the Edit modal to upload parity with the Upload modal: re-upload a
thumbnail or video file instead of only pasting URLs.

- Wire storage services (r2/s3/storageService) + pubkey/npub accessors into
  EditModal via ModalManager/initEditModal; EditModal constructs a shared
  MediaUploader.
- New editModalUpload.js holds all the upload glue (file-picker wiring, progress,
  storage-unlock checks, field write-back) to keep EditModal under its file-size
  budget. EditModal calls initEditModalUpload(this, context) in one line.
- edit-video-modal.html: "Replace video file…" (under the URL field) and
  "Replace thumbnail file…" (under the thumbnail field), each with a hidden file
  input + status line.
- On thumbnail upload: writes the new URL into the thumbnail field. On video
  upload: writes url + magnet (+ ws/xs hints). All written via setFieldUnlocked,
  which marks the field edited so EditModal.collect actually persists it (gated
  behind storage being configured + unlocked).

setFieldUnlocked is unit-tested (mutation-verified): without the unlock, the
re-upload would silently not save. Build + full lint + unit suite green.

NOTE: the upload/storage flow itself can't be unit-tested (browser + R2/S3);
pending manual verification of editing a video's thumbnail/file.

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

components/edit-video-modal.html

@@ -672,6 +672,26 @@
                 Edit field
               </button>
             </div>
+            <div class="flex items-center gap-2 flex-wrap">
+              <input type="file" id="editVideoFile" accept="video/*" class="hidden" />
+              <button
+                type="button"
+                id="editVideoFileBtn"
+                class="btn-ghost focus-ring text-xs"
+              >
+                Replace video file…
+              </button>
+              <p
+                id="editVideoUploadStatus"
+                class="text-2xs text-muted empty:hidden"
+                role="status"
+                aria-live="polite"
+              ></p>
+            </div>
+            <p class="text-xs text-muted">
+              Uploading a new file replaces the URL, magnet, and torrent hints.
+              Requires unlocked storage.
+            </p>
           </div>
 
           <div class="space-y-1">
@@ -760,6 +780,22 @@
                 Edit field
               </button>
             </div>
+            <div class="flex items-center gap-2 flex-wrap">
+              <input type="file" id="editThumbnailFile" accept="image/*" class="hidden" />
+              <button
+                type="button"
+                id="editThumbnailFileBtn"
+                class="btn-ghost focus-ring text-xs"
+              >
+                Replace thumbnail file…
+              </button>
+              <p
+                id="editThumbnailUploadStatus"
+                class="text-2xs text-muted empty:hidden"
+                role="status"
+                aria-live="polite"
+              ></p>
+            </div>
           </div>
 
           <div class="space-y-1">