Add release chat command — build sled binary and publish artifact

Finds the registered project carrying the huskies source tree, runs
`cargo build --release` inside its container (dedicated
CARGO_TARGET_DIR=target/sled-release so container builds stop
clobbering host target/release), then atomically publishes the binary
to ~/.huskies/artifacts/ with a .hash sidecar for convergence checks.

Full fleet redeploy is now chat-only: `release` then `upgrade all` —
no laptop access needed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019fHdm92yjvguPi2LiXfLB9

server/src/chat/transport/matrix/mod.rs

@@ -37,6 +37,8 @@ pub mod project_rebuild;
 pub mod projects;
 /// Rebuild command — triggers a server rebuild/restart via a bot command.
 pub mod rebuild;
+/// `release` gateway chat command — build the sled binary and publish it.
+pub mod release;
 /// Reset command — handles `!reset` bot commands to restart the server state.
 pub mod reset;
 /// rmtree command — handles `!rmtree` bot commands to remove worktrees.