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/startup.rs

@@ -11,6 +11,7 @@ use std::{
 };
 
 use futures::FutureExt as _;
+use lanspread_db::db::GameCatalog;
 use tokio::sync::{
     RwLock,
     mpsc::{UnboundedReceiver, UnboundedSender},
@@ -84,7 +85,8 @@ pub(crate) fn spawn_peer_runtime(
     game_dir: PathBuf,
     state_dir: PathBuf,
     unpacker: Arc<dyn Unpacker>,
-    catalog: Arc<RwLock<std::collections::HashSet<String>>>,
+    catalog: Arc<RwLock<GameCatalog>>,
+    active_outbound_transfers: crate::context::OutboundTransfers,
 ) -> PeerRuntimeHandle {
     let shutdown = CancellationToken::new();
     let task_tracker = TaskTracker::new();
@@ -104,6 +106,7 @@ pub(crate) fn spawn_peer_runtime(
             runtime_shutdown.clone(),
             runtime_tracker.clone(),
             catalog,
+            active_outbound_transfers,
         )
         .await
         {
@@ -190,6 +193,7 @@ fn spawn_peer_discovery_service(ctx: &Ctx, tx_notify_ui: &UnboundedSender<PeerEv
 fn spawn_peer_liveness_service(ctx: &Ctx, tx_notify_ui: &UnboundedSender<PeerEvent>) {
     let tx_notify_ui = tx_notify_ui.clone();
     let peer_game_db = ctx.peer_game_db.clone();
+    let catalog = ctx.catalog.clone();
     let active_operations = ctx.active_operations.clone();
     let active_downloads = ctx.active_downloads.clone();
     let shutdown = ctx.shutdown.clone();
@@ -207,6 +211,7 @@ fn spawn_peer_liveness_service(ctx: &Ctx, tx_notify_ui: &UnboundedSender<PeerEve
         move || {
             let tx_notify_ui = tx_notify_ui.clone();
             let peer_game_db = peer_game_db.clone();
+            let catalog = catalog.clone();
             let active_operations = active_operations.clone();
             let active_downloads = active_downloads.clone();
             let shutdown = shutdown.clone();
@@ -215,6 +220,7 @@ fn spawn_peer_liveness_service(ctx: &Ctx, tx_notify_ui: &UnboundedSender<PeerEve
                 run_ping_service(
                     tx_notify_ui,
                     peer_game_db,
+                    catalog,
                     active_operations,
                     active_downloads,
                     shutdown,