feat(fof-layer1): Tauri commands + frontend UI for vouches

Node helpers (crates/core/src/node.rs):
- vouch_for_peer(target): derives target X25519 pub from NodeId,
  inserts into own_vouch_targets, republishes bio post so the new
  VouchGrantBatch propagates to the receiver via CDN.
- revoke_vouch_and_rotate(target): per Scott's design, revocation IS
  the rotation primitive. Marks target current=0, generates new V_me
  epoch in vouch_keys_own (prior retained, Layer 4 receiver-chain),
  republishes bio. Revoked persona retains old V_me → grandfathered
  access to old content; locked out of new content sealed under V_new.
- list_vouches_given / list_vouches_received: enriched with display
  names via resolve_display_name.

Tauri commands (crates/tauri-app/src/lib.rs):
- vouch_for_peer, revoke_vouch_for_peer (single-action commands)
- list_vouches_given, list_vouches_received (DTOs with camelCase)
- All registered in the generate_handler! list.

Frontend (frontend/index.html + app.js):
- New "Vouches" section in Settings tab with side-by-side Given /
  Received lists. Per-row Revoke button on Given entries with confirm
  prompt explaining the rotation semantics.
- Bio modal gains Vouch / Revoke Vouch button next to Follow/Unfollow.
  State derived from list_vouches_given on modal open.
- loadVouches wired into the settings-tab activation handler.

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

crates/tauri-app/src/lib.rs

@@ -1089,6 +1089,62 @@ async fn list_ignored_peers(state: State<'_, AppNode>) -> Result<Vec<IgnoredPeer
     Ok(out)
 }
 
+// --- FoF Layer 1: Vouches ---
+
+#[derive(Serialize)]
+#[serde(rename_all = "camelCase")]
+struct VouchGivenDto {
+    node_id: String,
+    display_name: String,
+    granted_at_ms: u64,
+}
+
+#[derive(Serialize)]
+#[serde(rename_all = "camelCase")]
+struct VouchReceivedDto {
+    node_id: String,
+    display_name: String,
+    epoch: u32,
+    received_at_ms: u64,
+}
+
+#[tauri::command]
+async fn vouch_for_peer(state: State<'_, AppNode>, node_id_hex: String) -> Result<(), String> {
+    let node = get_node(&state).await;
+    let nid = parse_node_id(&node_id_hex)?;
+    node.vouch_for_peer(&nid).await.map_err(|e| e.to_string())
+}
+
+#[tauri::command]
+async fn revoke_vouch_for_peer(state: State<'_, AppNode>, node_id_hex: String) -> Result<(), String> {
+    let node = get_node(&state).await;
+    let nid = parse_node_id(&node_id_hex)?;
+    node.revoke_vouch_and_rotate(&nid).await.map_err(|e| e.to_string())
+}
+
+#[tauri::command]
+async fn list_vouches_given(state: State<'_, AppNode>) -> Result<Vec<VouchGivenDto>, String> {
+    let node = get_node(&state).await;
+    let rows = node.list_vouches_given().await.map_err(|e| e.to_string())?;
+    Ok(rows.into_iter().map(|(nid, name, at)| VouchGivenDto {
+        node_id: hex::encode(nid),
+        display_name: name,
+        granted_at_ms: at,
+    }).collect())
+}
+
+#[tauri::command]
+async fn list_vouches_received(state: State<'_, AppNode>) -> Result<Vec<VouchReceivedDto>, String> {
+    let node = get_node(&state).await;
+    let rows = node.list_vouches_received().await.map_err(|e| e.to_string())?;
+    Ok(rows.into_iter().map(|(nid, name, epoch, at)| VouchReceivedDto {
+        node_id: hex::encode(nid),
+        display_name: name,
+        epoch,
+        received_at_ms: at,
+    }).collect())
+}
+
 #[tauri::command]
 async fn list_follows(state: State<'_, AppNode>) -> Result<Vec<PeerDto>, String> {
     let node = get_node(&state).await;
@@ -3103,6 +3159,10 @@ pub fn run() {
             ignore_peer,
             unignore_peer,
             list_ignored_peers,
+            vouch_for_peer,
+            revoke_vouch_for_peer,
+            list_vouches_given,
+            list_vouches_received,
             list_circles,
             create_circle,
             delete_circle,