feat: add build version with timestamp

- Add build.rs to generate BUILD_VERSION at compile time
- Update CLI to show full version: '0.1.0 (build: 2026-03-31 11:21:37)'
- Update health endpoints to return build version
- Add chrono as build dependency

build.rs

@@ -0,0 +1,19 @@
+use chrono::Local;
+use std::env;
+
+fn main() {
+    let now = Local::now();
+    let build_time = now.format("%Y-%m-%d %H:%M:%S").to_string();
+
+    // Get version from Cargo.toml
+    let version = env!("CARGO_PKG_VERSION");
+    let full_version = format!("{} (build: {})", version, build_time);
+
+    // Set build-time environment variables
+    println!("cargo:rustc-env=BUILD_VERSION={}", full_version);
+    println!("cargo:rustc-env=BUILD_TIME={}", build_time);
+    println!("cargo:rustc-env=VERSION={}", version);
+
+    // Also print for debugging
+    println!("cargo:warning=Building version: {}", full_version);
+}