P2: peers CRUD and aggregated stats

Backend
- api/peers.rs: list/add/remove + aggregate() that derives totals,
  per-state counts, and tx/rx sums in one pass over the peer list
- poller.rs spawns a 3s tokio loop that emits peers://updated and
  stats://updated; cancelled via abort() on stop_daemon
- DELETE peer URL-encodes the endpoint (the path includes ://) with
  a small inline percent-encoder to avoid a url crate dep
- Tauri commands: peers_list, peer_add (with empty-string guard),
  peer_remove, peers_stats

Frontend
- peers store subscribes to the two events and refreshes after
  add/remove for immediate UI feedback
- Peers view renders endpoint, type, color-coded state badge, and
  formatBytes-formatted rx/tx; the four stat cards re-use a
  reusable Stat component
- AddPeerDialog uses radix-vue's Dialog primitive with regex
  validation for tcp:// and quic:// schemes

src-tauri/src/api/mod.rs

@@ -1,4 +1,5 @@
 pub mod admin;
+pub mod peers;
 
 use crate::error::{AppError, AppResult};
 use reqwest::{Client, Response};
@@ -48,7 +49,6 @@ impl MyceliumClient {
         }
     }
 
-    #[allow(dead_code)] // wired in P2 (peers add/remove)
     pub(crate) async fn check_status(resp: Response) -> AppResult<()> {
         let status = resp.status();
         if status.is_success() {