Logging level overhaul: reduce verbosity at info and debug levels

Per-packet happy-path events (UDP send/receive, TUN I/O, MMP report
processing, TreeAnnounce/FilterAnnounce sent, RTT samples) moved from
debug to trace. Periodic maintenance and retry scheduling moved from
info to debug. Session state changes (established, initiated, torn
down) and transport stop promoted from debug to info. MMP report send
failures demoted from warn to debug (normal under churn).

src/node/tree.rs

@@ -7,7 +7,7 @@ use crate::protocol::TreeAnnounce;
 use crate::NodeAddr;
 
 use super::{Node, NodeError};
-use tracing::{debug, info, warn};
+use tracing::{debug, info, trace, warn};
 
 impl Node {
     /// Build a TreeAnnounce from our current tree state.
@@ -68,7 +68,7 @@ impl Node {
             peer.record_tree_announce_sent(now_ms);
         }
 
-        debug!(peer = %peer_addr, "Sent TreeAnnounce");
+        trace!(peer = %peer_addr, "Sent TreeAnnounce");
         Ok(())
     }