Add /version endpoint and GitHub Actions release workflow

src/routes/mod.rs

@@ -1 +1,2 @@
 pub mod emotes;
+pub mod version;

src/routes/version.rs

@@ -0,0 +1,25 @@
+use axum::response::{IntoResponse, Json};
+use serde_json::json;
+
+/// GET /version
+/// Returns the current git commit hash and tag (if present).
+pub async fn version() -> impl IntoResponse {
+    let commit = env!("GIT_COMMIT_HASH");
+    let tag = env!("GIT_TAG");
+
+    // `git describe --tags --exact-match` sets an exact semver-like tag when the
+    // commit is tagged; otherwise the build script stores "untagged".
+    let response = if tag == "untagged" {
+        json!({
+            "commit": commit,
+            "version": null
+        })
+    } else {
+        json!({
+            "commit": commit,
+            "version": tag
+        })
+    };
+
+    Json(response)
+}