refactor(peer): tighten listener-addr handshake invariant

Follow-up hardening for 348a02c, where `listen_addr` was added to Hello and
HelloAck as `Option<SocketAddr>`. Code review surfaced three concrete problems
that the previous commit left open:

1. Cold-start asymmetry. Discovery and the QUIC/mDNS advertiser are spawned
   concurrently. If discovery saw a cached peer advertisement before our own
   advertiser had written `ctx.local_peer_addr`, our outbound Hello carried
   `listen_addr: None`. The receiver's `peer_record_addr` then returned `None`
   and silently dropped the Hello while we still recorded their HelloAck, so
   peer A learned about peer B but B never learned about A until a later
   handshake happened to win the race.

2. Duplicate game-list pipeline. The previous commit added
   `refresh_peer_games`, which post-handshake issued a `ListGames` to fetch
   `peer.games`. The library-sync path (`LibrarySnapshot`) already populates
   the same field. Both could race on first contact and overwrite each other.
   Worse, `refresh_peer_games` was misnamed: a `peer_game_count > 0` guard
   turned it into a fetch-once-then-no-op helper, while
   `handle_library_summary` independently re-triggered a full handshake when
   `previous_count == 0` was observed, producing a redundant ping-pong on
   every first contact.

3. Argument explosion. `perform_handshake_with_peer`, `spawn_library_resync`,
   and `after_peer_library_recorded` had grown to 6-8 individual parameters
   and acquired `#[allow(clippy::too_many_arguments)]` opt-outs. Every caller
   was destructuring the same fields out of `Ctx`/`PeerCtx`.

Changes (all in one commit because they jointly enforce the same invariant:
"a peer is only ever recorded by its listener address, and the local
listener address must exist before we participate in the protocol"):

- `Hello.listen_addr` and `HelloAck.listen_addr` are now `SocketAddr`, not
  `Option<SocketAddr>`. Wire-incompatible, but PROTOCOL_VERSION already moved
  to 3 in 348a02c so no additional version bump is needed.
- `required_listen_addr` reads `ctx.local_peer_addr` and returns an
  `eyre::Result`; `build_hello_from_state` and `build_hello_ack` both call
  it, so an outbound or inbound Hello can no longer be constructed before
  the local QUIC listener is bound. The inbound path maps this into a
  `Response::InternalPeerError` so the remote peer fails cleanly instead of
  seeing a malformed HelloAck.
- `run_peer_discovery` blocks on `wait_for_local_peer_addr` (25 ms poll,
  shutdown-aware) before subscribing to the mDNS browser. This closes the
  cold-start race for outbound handshakes at the source.
- `refresh_peer_games`, `request_game_list_from_peer`, and the
  `previous_count == 0` re-handshake trigger are removed. The post-handshake
  flow now relies solely on `LibrarySummary`/`LibrarySnapshot`/`LibraryDelta`
  for peer-library state; `ListGames` survives only for the
  `request_game_details_*` paths that fetch per-game file descriptions on
  demand.
- New `HandshakeCtx` (with `from_ctx` and `from_peer_ctx` constructors)
  replaces the long argument lists. All `too_many_arguments` allow-attrs in
  `handshake.rs` are gone, and call sites in `handlers.rs`, `discovery.rs`,
  and `stream.rs` collapse to a single clone.
- `handle_library_delta` no longer acquires a read lock on the apply path:
  the `peer_addr` lookup moved into the `else` resync branch where it is
  actually needed.
- `accept_inbound_hello`'s `remote_addr` parameter is renamed to
  `transport_addr`. It is now used only for warn-log formatting, and the
  new name signals that this is the ephemeral QUIC source port, never the
  authoritative listener address that gets recorded.

User-visible effect: on cold start, peers can no longer end up with an
asymmetric view of each other ("A sees B but B never sees A"). First-contact
library sync now does one handshake plus one snapshot/delta exchange instead
of the previous handshake + ListGames + redundant follow-up handshake. The
direct-connect CLI path (`handle_connect_peer_command`) now fails fast with
"local peer listener address is not ready" if invoked before the QUIC server
has bound; this is intentional - the previous behaviour would have sent a
Hello that the receiver had to silently discard.

Test Plan:
- just fmt
- just clippy
- just test (80 peer + 3 cli + 5 tauri tests pass)
- just build
- Manual: bring up `just peer-cli-alpha`/`bravo`/`charlie`, confirm symmetric
  peer discovery and that games show up on every side after one library
  digest cycle, with no duplicated ListGames traffic in trace logs.

Refs: Review feedback on commit 348a02c (listener-address handshake fix).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/lanspread-peer/src/network.rs

@@ -8,7 +8,7 @@ use std::{
 use bytes::BytesMut;
 use futures::{SinkExt, StreamExt};
 use if_addrs::{IfAddr, Interface, get_if_addrs};
-use lanspread_db::db::{Game, GameFileDescription};
+use lanspread_db::db::GameFileDescription;
 use lanspread_proto::{
     Hello,
     HelloAck,
@@ -172,33 +172,6 @@ pub async fn send_goodbye(peer_addr: SocketAddr, peer_id: String) -> eyre::Resul
     send_oneway_request(peer_addr, Request::Goodbye { peer_id }).await
 }
 
-/// Requests the current game list from a peer.
-pub async fn request_game_list_from_peer(peer_addr: SocketAddr) -> eyre::Result<Vec<Game>> {
-    let mut conn = connect_to_peer(peer_addr).await?;
-
-    let stream = conn.open_bidirectional_stream().await?;
-    let (rx, tx) = stream.split();
-    let mut framed_rx = FramedRead::new(rx, LengthDelimitedCodec::new());
-    let mut framed_tx = FramedWrite::new(tx, LengthDelimitedCodec::new());
-
-    framed_tx.send(Request::ListGames.encode()).await?;
-    framed_tx.close().await?;
-
-    let mut data = BytesMut::new();
-    while let Some(Ok(bytes)) = framed_rx.next().await {
-        data.extend_from_slice(&bytes);
-    }
-
-    let response = Response::decode(data.freeze());
-    match response {
-        Response::ListGames(games) => Ok(games),
-        Response::InternalPeerError(error_msg) => {
-            eyre::bail!("peer {peer_addr} reported internal error: {error_msg}")
-        }
-        other => eyre::bail!("unexpected response from {peer_addr}: {other:?}"),
-    }
-}
-
 /// Requests game file details from a peer.
 pub async fn request_game_details_from_peer(
     peer_addr: SocketAddr,