feat(us-016): connection/heartbeat visibility for tracker and node

Tracker now prints a line when a node registers and on every heartbeat
received. Node prints its assigned node_id after successful registration
and starts a daemon heartbeat thread (30s interval) that logs each send.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/tracker/meshnet_tracker/server.py

@@ -656,6 +656,13 @@ class _TrackerHandler(http.server.BaseHTTPRequestHandler):
             if assignment_directive is not None:
                 entry.pending_directives.clear()
 
+        shard_info = f"layers {shard_start}-{shard_end}" if shard_start is not None else "unsharded"
+        repo_info = f" [{hf_repo}]" if hf_repo else ""
+        print(
+            f"[tracker] node registered: {node_id[:8]}  {endpoint}  {model}{repo_info}  {shard_info}",
+            flush=True,
+        )
+
         payload = {"node_id": node_id}
         if assignment_directive is not None:
             payload["directive"] = assignment_directive
@@ -673,6 +680,10 @@ class _TrackerHandler(http.server.BaseHTTPRequestHandler):
             _rebalance_model_locked(server, entry.model or "stub-model")
             directives = list(entry.pending_directives)
             entry.pending_directives.clear()
+        print(
+            f"[tracker] heartbeat: {node_id[:8]}  {entry.endpoint}",
+            flush=True,
+        )
         if directives:
             self._send_json(200, {"directives": directives})
         else: