Sharpen pilot logging: ISO timestamps, level labels, transport-error classification, per-frame info

- Emit ISO-8601 timestamps and string level labels (info/warn/...) so
  Portainer's log viewer renders seconds and human-readable levels.
- Classify ETIMEDOUT/ECONNRESET/EPIPE/ENOTCONN as info one-liners
  rather than warns with stack traces. These are routine on cellular.
- Add an info "frame ingested" line per accepted AVL frame so device
  activity is visible at info level until task 1.10 wires up prom-client.

src/observability/logger.ts

@@ -22,10 +22,19 @@ export function createLogger(options: {
     instance_id: instanceId,
   };
 
+  // Emit `"level":"info"` instead of pino's default `"level":30` so log
+  // viewers (Portainer, etc.) show a human-readable label rather than the
+  // numeric level.
+  const formatters = {
+    level: (label: string) => ({ level: label }),
+  };
+
   if (nodeEnv === 'development') {
     return pino({
       level,
       base,
+      timestamp: pino.stdTimeFunctions.isoTime,
+      formatters,
       transport: {
         target: 'pino-pretty',
         options: {
@@ -37,6 +46,8 @@ export function createLogger(options: {
     });
   }
 
-  // Production and test: plain JSON — fast, no extra deps
-  return pino({ level, base });
+  // Production and test: plain JSON — fast, no extra deps.
+  // ISO-8601 string timestamps (vs default epoch-ms) survive downstream
+  // log renderers (Portainer, Docker --timestamps) without losing seconds.
+  return pino({ level, base, timestamp: pino.stdTimeFunctions.isoTime, formatters });
 }