build: track git HEAD and index in build script to accurately detect dirty state

server/build.rs

@@ -23,6 +23,8 @@ fn main() {
 
     let version = format!("{build_date} ({git_hash})");
     println!("cargo:rustc-env=APP_VERSION={version}");
+    println!("cargo:rerun-if-changed=../.git/HEAD");
+    println!("cargo:rerun-if-changed=../.git/index");
 
     if std::env::var("CARGO_CFG_TARGET_OS").unwrap_or_default() == "windows" {
         let mut res = winres::WindowsResource::new();