feat: peer version exchange with soft-warn UI indicator

Adds a one-shot Hello message to the lan-mouse wire protocol so each
peer can display the other end's build commit hash and warn on
version mismatch. Soft-warn only — mismatched versions never refuse
traffic.

Wire change (lan-mouse-proto)
* `ProtoEvent::Hello { commit: [u8; 8] }` carries the 8-byte ASCII
  short commit from shadow_rs's `SHORT_COMMIT`. Encoded/decoded
  alongside the existing event variants.
* `EventType::Hello` is appended to the enum so existing IDs are
  untouched. Old peers receive the event, hit `InvalidEventId`, and
  silently skip it via the forward-compat handler in
  `connect.rs::receive_loop` — the connection is unaffected.

Daemon
* Connect side sends one Hello immediately after the DTLS handshake
  authenticates and before the ping_pong loop starts. Best-effort,
  fire-and-forget — `log::debug!` on send error.
* Listen side mirrors the peer's Hello with its own (same shape as
  the existing Ping → Pong reply), so the peer's connect-side
  receive_loop populates `ClientState::peer_commit` for that
  handle.
* The disconnect path clears `peer_commit` so a stale hash isn't
  shown after the connection drops.

IPC
* `ClientState::peer_commit: Option<[u8; 8]>`. `None` means the
  peer hasn't sent Hello yet — either fresh connection or older
  build that predates the event.

GTK
* `ClientObject` exposes `peer-commit` as an `Option<String>`
  property; `peer_commit_to_string` converts the wire `[u8; 8]` to
  the displayable hex.
* `lan_mouse_gtk::run` now takes the local commit and stashes it in
  a `OnceLock` so per-row UI can compare against each peer's hash.
* `ClientRow::refresh_version_status` re-renders the collapsed
  subtitle with Pango markup whenever the property changes:
   - matched → green   "peer version: <hex> · matched"
   - mismatch → orange "peer version: <hex> · ours: <hex>"
   - unknown → orange  "peer version: unknown · ours: <hex>"
* Window invokes `refresh_version_status` from
  `update_client_state` after writing the new property, and
  `bind` calls it once on row construction so the initial
  subtitle isn't blank.

Known limitation: state-change broadcasts from the network side
(set_alive / set_active_addr / set_peer_commit) don't currently
trigger a `FrontendEvent::State` directly; the UI picks up the
latest values on the next user-driven broadcast. Same pre-existing
behavior as the alive/active_addr fields.

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

src/emulation.rs

@@ -1,3 +1,4 @@
+use crate::config::local_commit;
 use crate::listen::{LanMouseListener, ListenEvent, ListenerCreationError};
 use futures::StreamExt;
 use input_emulation::{EmulationHandle, InputEmulation, InputEmulationError};
@@ -150,6 +151,16 @@ impl ListenTask {
                             }
                             ProtoEvent::Input(event) => self.emulation_proxy.consume(event, addr),
                             ProtoEvent::Ping => self.listener.reply(addr, ProtoEvent::Pong(self.emulation_proxy.emulation_active.get())).await,
+                            // Mirror the peer's version handshake. The
+                            // outgoing connect side initiated this with
+                            // its own Hello; we echo ours back so the
+                            // peer's connect-side receive_loop can
+                            // populate `peer_commit`. We don't store
+                            // the peer's commit on the listen side —
+                            // the user-visible state lives on outgoing
+                            // connections, where the same peer is also
+                            // configured as a `[[clients]]` entry.
+                            ProtoEvent::Hello { .. } => self.listener.reply(addr, ProtoEvent::Hello { commit: local_commit() }).await,
                             _ => {}
                         }
                     }