fix(peer): settle current-protocol local state cleanup

The follow-up backlog had drifted into three settled peer/runtime issues: the
legacy game-list fallback contradicted the one-wire-version policy, the Tauri
shell still re-derived local install state from disk after peer snapshots, and
`Availability::Downloading` existed even though active operations are already
reported through a separate operation table.

Remove the legacy `AnnounceGames` request and fallback service. Discovery now
ignores peers that do not advertise the current protocol and a peer id, and
library changes are sent through the current delta path only. This keeps the
runtime aligned with the documented current-build-only interoperability model.

Make peer `LocalGamesUpdated` snapshots authoritative for local fields in the
Tauri database. The GUI-side catalog still owns static metadata such as names,
sizes, and descriptions, but downloaded, installed, local version, and
availability now come from the peer runtime instead of a second whole-library
filesystem scan. Snapshot reconciliation also pins the missing-begin and
missing-finish lifecycle cases in tests.

Collapse availability back to the settled `Ready` and `LocalOnly` states.
Aggregation now counts only `Ready` peers as download sources, and the frontend
no longer carries a dead `Downloading` enum value.

The core peer also exposes the small non-GUI hooks needed by scripted callers:
startup options for state and mDNS, a local-ready event, direct connection, peer
snapshots, and an explicit post-download install policy. Those hooks reuse the
same current protocol path and do not add compatibility shims.

Test Plan:
- `git diff --check`
- `just fmt`
- `just clippy`
- `just test`

Refs: BACKLOG.md, FINDINGS.md, IMPL_DECISIONS.md

crates/lanspread-peer/src/services/stream.rs

@@ -9,13 +9,12 @@ use s2n_quic::stream::{BidirectionalStream, SendStream};
 use tokio_util::codec::{FramedRead, FramedWrite, LengthDelimitedCodec};
 
 use crate::{
-    PeerEvent,
     context::PeerCtx,
     error::PeerError,
     events,
     local_games::{get_game_file_descriptions, is_local_dir_name, local_download_available},
     peer::{send_game_file_chunk, send_game_file_data},
-    remote_peer::{ensure_peer_id_for_addr, update_peer_from_game_list},
+    remote_peer::ensure_peer_id_for_addr,
     services::handshake::{
         accept_inbound_hello,
         perform_handshake_with_peer,
@@ -113,10 +112,6 @@ async fn dispatch_request(
             log::error!("Received invalid request from peer");
             framed_tx
         }
-        Request::AnnounceGames(games) => {
-            handle_announce_games(ctx, remote_addr, games).await;
-            framed_tx
-        }
     }
 }
 
@@ -381,18 +376,6 @@ async fn handle_goodbye(ctx: &PeerCtx, remote_addr: Option<SocketAddr>, peer_id:
     events::emit_peer_game_list(&ctx.peer_game_db, &ctx.tx_notify_ui).await;
 }
 
-async fn handle_announce_games(ctx: &PeerCtx, remote_addr: Option<SocketAddr>, games: Vec<Game>) {
-    log::info!(
-        "Received {} announced games from peer {remote_addr:?}",
-        games.len()
-    );
-
-    if let Some(addr) = remote_addr {
-        let aggregated_games = update_peer_from_game_list(&ctx.peer_game_db, addr, &games).await;
-        events::send(&ctx.tx_notify_ui, PeerEvent::ListGames(aggregated_games));
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use std::{
@@ -438,6 +421,7 @@ mod tests {
             CancellationToken::new(),
             TaskTracker::new(),
             Arc::new(RwLock::new(catalog)),
+            true,
         )
         .to_peer_ctx(tx_notify_ui)
     }