feat: add detailed --version output with build-time version injection

build.rs

@@ -0,0 +1,19 @@
+use std::process::Command;
+
+fn main() {
+    let version = std::env::var("CCSM_VERSION")
+        .unwrap_or_else(|_| env!("CARGO_PKG_VERSION").to_string());
+
+    let commit = Command::new("git")
+        .args(["rev-parse", "--short", "HEAD"])
+        .output()
+        .ok()
+        .and_then(|o| String::from_utf8(o.stdout).ok())
+        .map(|s| s.trim().to_string())
+        .unwrap_or_else(|| "unknown".to_string());
+
+    println!("cargo:rustc-env=CCSM_VERSION={version}");
+    println!("cargo:rustc-env=GIT_COMMIT_SHORT={commit}");
+    println!("cargo:rerun-if-changed=.git/HEAD");
+    println!("cargo:rerun-if-env-changed=CCSM_VERSION");
+}