[feat](trx-rs): show server/client build info in HTTP footer

Add compile-time build dates for trx-server and trx-frontend-http, propagate server build metadata through rig state/snapshot, and render both versions + build dates in the HTTP footer.

Co-authored-by: OpenAI Codex <codex@openai.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>

src/trx-server/build.rs

@@ -0,0 +1,25 @@
+use std::time::{SystemTime, UNIX_EPOCH};
+
+fn utc_ymd_from_unix_secs(secs: i64) -> (i32, u32, u32) {
+    let days = secs.div_euclid(86_400);
+    let z = days + 719_468;
+    let era = if z >= 0 { z } else { z - 146_096 } / 146_097;
+    let doe = z - era * 146_097;
+    let yoe = (doe - doe / 1_460 + doe / 36_524 - doe / 146_096) / 365;
+    let mut y = yoe + era * 400;
+    let doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
+    let mp = (5 * doy + 2) / 153;
+    let d = doy - (153 * mp + 2) / 5 + 1;
+    let m = mp + if mp < 10 { 3 } else { -9 };
+    y += if m <= 2 { 1 } else { 0 };
+    (y as i32, m as u32, d as u32)
+}
+
+fn main() {
+    let secs = match SystemTime::now().duration_since(UNIX_EPOCH) {
+        Ok(d) => d.as_secs() as i64,
+        Err(_) => 0,
+    };
+    let (y, m, d) = utc_ymd_from_unix_secs(secs);
+    println!("cargo:rustc-env=TRX_SERVER_BUILD_DATE={y:04}-{m:02}-{d:02}");
+}