feat(peer): coordinate outbound transfers with local game mutations

Updating or removing a local game rewrites its on-disk files. Peers that
were mid-download of that game would keep streaming bytes from files that
are being deleted or replaced, handing them a corrupt or stale copy.
There was also no authoritative notion of which game version a peer
should serve or accept, so a peer could serve whatever happened to be on
disk and downloaders could aggregate files from peers running mismatched
versions.

This introduces a reader-writer coordination scheme between outbound file
transfers (readers) and local mutation operations (writers), and gates
both serving and downloading on an authoritative game catalog version.

Reader-writer coordination:
- Track active outbound transfers per game in a shared `OutboundTransfers`
  map of (id, CancellationToken), threaded through `Ctx`/`PeerCtx` and
  registered by a `TransferGuard` in the stream service. The guard is
  registered *before* the serve-eligibility check to close a TOCTOU window
  where a writer could miss an in-flight reader.
- `stream_file_bytes` now honors a cancellation token at every await point
  (file read, network send, stream close) via `tokio::select!`, so a
  transfer aborts promptly instead of hanging on a stalled receiver.
- `begin_operation` marks a game active first, then cancels its outbound
  transfers and waits for the count to reach zero before any
  Updating/RemovingDownload work touches the filesystem.
- Active games are now hidden from library snapshots entirely while an
  operation is in flight, instead of freezing their last announced state,
  so peers stop discovering a game that is being mutated.

Authoritative version catalog:
- Replace the `HashSet<String>` catalog with `GameCatalog`, mapping each
  game id to its expected version (from the bundled game.db / ETI data).
- Serving requires the local `version.ini` to match the catalog version
  (`local_download_matches_catalog`); peer selection, file aggregation,
  and majority size validation all filter on the expected version
  (`peers_with_expected_version`, `aggregated_game_files`, and friends).

User-visible changes:
- The GUI shows confirmation dialogs before Update and Remove, and
  surfaces a sharing-status indicator on game cards and the detail modal.
- A new `OutboundTransferCountChanged` event lets the UI reflect live
  outbound transfer activity.

Test Plan:
- just test
- just frontend-test
- just clippy

crates/lanspread-peer/src/events.rs

@@ -2,6 +2,7 @@
 
 use std::{collections::HashMap, net::SocketAddr, sync::Arc};
 
+use lanspread_db::db::GameCatalog;
 use tokio::sync::{RwLock, mpsc::UnboundedSender};
 
 use crate::{
@@ -65,9 +66,13 @@ fn active_operation_kind(operation: OperationKind) -> ActiveOperationKind {
 
 pub async fn emit_peer_game_list(
     peer_game_db: &Arc<RwLock<PeerGameDB>>,
+    catalog: &Arc<RwLock<GameCatalog>>,
     tx_notify_ui: &UnboundedSender<PeerEvent>,
 ) {
-    let games = { peer_game_db.read().await.get_all_games() };
+    let games = {
+        let catalog = catalog.read().await;
+        peer_game_db.read().await.get_catalog_games(&catalog)
+    };
     send(tx_notify_ui, PeerEvent::ListGames(games));
 }