feat: initial rusty-telemetry UDP listener

- Async UDP listener on configurable bind address (default 127.0.0.1:5005)
- RUSTY_TELEMETRY_BIND env var for cross-machine deployment
- Deserializes JSON telemetry frames with serde
- deny_unknown_fields for schema drift detection
- ReceiveStats tracker with packet rate and data rate
- Locked stdout writes for efficient output
- .gitignore for /target/ and .idea/

src/main.rs

@@ -0,0 +1,78 @@
+mod stats;
+mod telemetry;
+
+use stats::ReceiveStats;
+use telemetry::TelemetryFrame;
+
+use std::io::Write;
+
+const DEFAULT_BIND_ADDR: &str = "127.0.0.1:5005";
+const BUFFER_SIZE: usize = 65535;
+
+fn print_banner(bind_addr: &str) {
+    println!("========================================");
+    println!("  rusty-telemetry listener");
+    println!("  Phase 1 - UDP JSON receiver");
+    println!("========================================");
+    println!("  Bind: {}", bind_addr);
+    println!("========================================");
+    println!();
+}
+
+#[tokio::main]
+async fn main() {
+    let bind_addr =
+        std::env::var("RUSTY_TELEMETRY_BIND").unwrap_or_else(|_| DEFAULT_BIND_ADDR.to_string());
+
+    print_banner(&bind_addr);
+
+    let socket = match tokio::net::UdpSocket::bind(&bind_addr).await {
+        Ok(s) => {
+            let local_addr = s.local_addr().unwrap();
+            println!("[INFO] Listening on {}", local_addr);
+            s
+        }
+        Err(e) => {
+            eprintln!("[ERROR] Failed to bind UDP socket: {}", e);
+            std::process::exit(1);
+        }
+    };
+
+    let mut buf = vec![0u8; BUFFER_SIZE];
+    let mut stats = ReceiveStats::new();
+    let stdout = std::io::stdout();
+
+    loop {
+        match socket.recv_from(&mut buf).await {
+            Ok((len, src)) => {
+                stats.record(len);
+
+                let text = match std::str::from_utf8(&buf[..len]) {
+                    Ok(s) => s,
+                    Err(e) => {
+                        eprintln!("[WARN] Invalid UTF-8 from {}: {}", src, e);
+                        continue;
+                    }
+                };
+
+                let frame: TelemetryFrame = match serde_json::from_str(text) {
+                    Ok(f) => f,
+                    Err(e) => {
+                        eprintln!("[WARN] JSON parse error from {}: {}", src, e);
+                        continue;
+                    }
+                };
+
+                {
+                    let mut handle = stdout.lock();
+                    let _ = writeln!(handle, "{}", frame);
+                    let _ = writeln!(handle, "  [{}] {}", src, stats);
+                    let _ = writeln!(handle);
+                }
+            }
+            Err(e) => {
+                eprintln!("[ERROR] Receive error: {}", e);
+            }
+        }
+    }
+}