add tracing, env config, dotenvy

bootstrap: tracing-subscriber with RUST_LOG env filter, ServerConfig
from env vars (KFRAME_DATABASE_URL, KFRAME_TCP_ADDR, etc.), dotenvy
for .env file loading. Replaced all println with tracing macros.

tcp-server: replaced println with tracing::info/warn.

Added .env.example and .gitignore for db files.

crates/adapters/tcp-server/Cargo.toml

@@ -9,3 +9,4 @@ protocol.workspace = true
 tokio.workspace = true
 postcard.workspace = true
 thiserror.workspace = true
+tracing.workspace = true

crates/adapters/tcp-server/src/server.rs

@@ -2,6 +2,7 @@ use std::sync::Arc;
 use tokio::net::TcpListener;
 use tokio::sync::broadcast;
 use tokio::io::AsyncWriteExt;
+use tracing::{info, warn};
 use crate::broadcaster::TcpBroadcaster;
 use crate::error::TcpServerError;
 
@@ -10,11 +11,11 @@ pub async fn run_tcp_server(
     broadcaster: Arc<TcpBroadcaster>,
 ) -> Result<(), TcpServerError> {
     let listener = TcpListener::bind(addr).await.map_err(TcpServerError::Io)?;
-    println!("TCP server listening on {addr}");
+    info!(addr, "TCP server listening");
 
     loop {
         let (mut socket, peer) = listener.accept().await.map_err(TcpServerError::Io)?;
-        println!("Client connected: {peer}");
+        info!(%peer, "client connected");
 
         let mut rx = broadcaster.subscribe();
 
@@ -23,13 +24,13 @@ pub async fn run_tcp_server(
                 match rx.recv().await {
                     Ok(frame) => {
                         if socket.write_all(&frame).await.is_err() {
-                            println!("Client disconnected: {peer}");
+                            info!(%peer, "client disconnected");
                             break;
                         }
                     }
                     Err(broadcast::error::RecvError::Closed) => break,
                     Err(broadcast::error::RecvError::Lagged(n)) => {
-                        println!("Client {peer} lagged by {n} messages");
+                        warn!(%peer, skipped = n, "client lagged");
                     }
                 }
             }