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/services/local_monitor.rs

@@ -336,12 +336,12 @@ fn should_ignore_game_child(name: &str) -> bool {
 #[cfg(test)]
 mod tests {
     use std::{
-        collections::HashSet,
         path::{Path, PathBuf},
         sync::Arc,
         time::Duration,
     };
 
+    use lanspread_db::db::GameCatalog;
     use notify::{
         EventKind,
         event::{AccessKind, AccessMode},
@@ -373,7 +373,7 @@ mod tests {
         std::fs::write(path, bytes).expect("file should be written");
     }
 
-    fn test_ctx(game_dir: PathBuf, catalog: HashSet<String>) -> Ctx {
+    fn test_ctx(game_dir: PathBuf, catalog: GameCatalog) -> Ctx {
         Ctx::new(
             Arc::new(RwLock::new(PeerGameDB::new())),
             "peer".to_string(),
@@ -383,6 +383,7 @@ mod tests {
             CancellationToken::new(),
             TaskTracker::new(),
             Arc::new(RwLock::new(catalog)),
+            Arc::new(RwLock::new(std::collections::HashMap::new())),
         )
     }
 
@@ -445,7 +446,7 @@ mod tests {
         let temp = TempDir::new("lanspread-local-monitor");
         let ctx = test_ctx(
             temp.path().to_path_buf(),
-            HashSet::from(["game".to_string()]),
+            GameCatalog::from_ids(["game".to_string()]),
         );
         ctx.active_operations
             .write()
@@ -480,7 +481,7 @@ mod tests {
         write_file(&temp.path().join("game").join("version.ini"), b"20250101");
         let ctx = test_ctx(
             temp.path().to_path_buf(),
-            HashSet::from(["game".to_string()]),
+            GameCatalog::from_ids(["game".to_string()]),
         );
         let gate = RescanGate::default();
         let (tx, mut rx) = mpsc::unbounded_channel();
@@ -515,7 +516,7 @@ mod tests {
         write_file(&game_root.join("version.ini"), b"20250101");
         let ctx = test_ctx(
             temp.path().to_path_buf(),
-            HashSet::from(["game".to_string()]),
+            GameCatalog::from_ids(["game".to_string()]),
         );
         let gate = RescanGate::default();
         let (tx, mut rx) = mpsc::unbounded_channel();
@@ -551,7 +552,7 @@ mod tests {
         write_file(&temp.path().join("game").join("version.ini"), b"20250101");
         let ctx = test_ctx(
             temp.path().to_path_buf(),
-            HashSet::from(["game".to_string()]),
+            GameCatalog::from_ids(["game".to_string()]),
         );
         let (tx, mut rx) = mpsc::unbounded_channel();
 
@@ -575,7 +576,7 @@ mod tests {
         );
         let ctx = test_ctx(
             temp.path().to_path_buf(),
-            HashSet::from(["game".to_string()]),
+            GameCatalog::from_ids(["game".to_string()]),
         );
         let (tx, mut rx) = mpsc::unbounded_channel();