feat(fof-layer3): Mode 1 publish + read + Tauri + UI wiring

End-to-end FoFClosed (Mode 1: encrypted body + FoF comments):

Node API:
- create_post_fof_closed(content) -> (PostId, Post, cek)
  Builds gating, encrypts body via fof::encrypt_fof_body, base64s it
  into post.content, stores with visibility=FoFClosed +
  intent=Public, propagates via update_neighbor_manifests_as.
- read_fof_closed_body(post_id) -> Option<String>
  Trial-unlocks via find_unlock_for_post, decrypts body, returns
  plaintext. Returns None for non-FoFClosed or non-member readers.

Tauri commands:
- create_post_fof_closed, read_fof_closed_body. Registered in
  generate_handler!.

Feed rendering:
- PostDto.visibility carries the new "fof-closed" string.
- renderPost(): FoFClosed posts render with a locked placeholder
  (data-fof-closed-pending=post_id span). Visual badge added.
- unlockFoFClosedPlaceholders(rootEl): post-render async pass that
  scans for placeholder spans and dispatches read_fof_closed_body
  for each. Fills in body for FoF readers; falls back to a
  "not in this FoF set" notice otherwise.
- Wired into feed-list and my-posts-list render paths.

Compose:
- "Body+Comments: FoF only (Mode 1)" option in comment-perm-select.
  Selected → dispatches to create_post_fof_closed.

CLI feed renderer + Tauri feed-DTO match arms updated to handle
FoFClosed.

New end-to-end test brings total to 146:
- fof_closed_body_end_to_end: Alice authors FoFClosed body; Bob (with
  Alice's V_me in his keyring) unlocks + decrypts; Carol (no
  matching V_x) cannot unlock and sees only ciphertext.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/index.html

@@ -105,6 +105,7 @@
                 <option value="public">Comments: All</option>
                 <option value="followers_only">Comments: Followers</option>
                 <option value="friends_of_friends">Comments: Friends of Friends</option>
+                <option value="fof_closed">Body+Comments: FoF only (Mode 1)</option>
                 <option value="none">Comments: Off</option>
               </select>
               <select id="react-perm-select" title="React permission">