chore: log version on startup and gitignore build_hash

Startup now logs "huskies v0.10.0 (build abc1234)" so we can verify
both the version and the commit that's running. build_hash is a
runtime artifact, not tracked in git.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -9,6 +9,7 @@
 store.json
 .huskies_port
 .huskies/bot.toml.bak
+.huskies/build_hash
 
 # Coverage report (generated by script/test_coverage, not tracked in git)
 .coverage_report.json

server/src/main.rs

@@ -183,10 +183,14 @@ async fn main() -> Result<(), std::io::Error> {
         }
     });
 
-    // Log the build hash so we can verify which commit is running.
+    // Log version and build hash so we can verify what's running.
     let build_hash = std::fs::read_to_string(".huskies/build_hash")
         .unwrap_or_else(|_| "unknown".to_string());
-    slog!("[startup] Running build: {}", build_hash.trim());
+    slog!(
+        "[startup] huskies v{} (build {})",
+        env!("CARGO_PKG_VERSION"),
+        build_hash.trim()
+    );
 
     let app_state = Arc::new(SessionState::default());
     let cwd = std::env::current_dir().unwrap_or_else(|_| PathBuf::from("."));