Administer the directory from iPX with an rwa token (#206)

A Directory feed's page offers Check now and Remove to an admin whose token is rwa (the page
learns it from can_admin on the feed's page, asked of the directory only for admins). Admin,
Directory lists the servers sharing, from a new GET /v1/instances, and the blocked feeds by
title: a feed is often blocked because its address carries a key, so the address stays in the
directory. Unblocking or dropping a snapshot sends this server's snapshot again at once; since
directory's 403 reaches the page as 403, not 502.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/directory/src/lib.rs

@@ -94,6 +94,14 @@ pub struct Me {
     pub access: Access,
 }
 
+/// A token whose snapshot the directory holds: how many feeds it gave, and how many people.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Instance {
+    pub name: String,
+    pub feeds: i64,
+    pub subscribers: i64,
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct Blocked {
     pub id: String,
@@ -242,6 +250,7 @@ pub fn router(dir: Shared) -> Router {
         .route("/v1/snapshot", post(snapshot))
         .route("/v1/blocked", get(blocked))
         .route("/v1/blocked/{id}", delete(unblock))
+        .route("/v1/instances", get(instances))
         .route("/v1/instances/{name}", delete(drop_instance))
         .layer(axum::middleware::from_fn_with_state(dir.clone(), authenticate));
     Router::new()
@@ -402,6 +411,11 @@ async fn unblock(State(dir): State<Shared>, Extension(me): Extension<Me>, Path(i
     Ok(StatusCode::NO_CONTENT)
 }
 
+async fn instances(State(dir): State<Shared>, Extension(me): Extension<Me>) -> Result<Json<Vec<Instance>>, ApiError> {
+    need(&me, Access::Rwa)?;
+    Ok(Json(dir.store.instances().await?))
+}
+
 async fn drop_instance(State(dir): State<Shared>, Extension(me): Extension<Me>, Path(name): Path<String>) -> Result<StatusCode, ApiError> {
     need(&me, Access::Rwa)?;
     let n = dir.store.drop_instance(&name).await?;