Step 5 (syslog): esp_log to remote syslog

- aes67_syslog: esp_log_set_vprintf hook chained to the UART; formats
  into a static buffer under a zero-timeout mutex (drop and count when
  busy), strips ANSI codes, parses level/tag, filters by log.level and
  queues (48 messages, non-blocking). Low-priority sender task: RFC 5424
  (<PRI>1 - HOST APP - - - MSG, no timestamp yet) or RFC 3164
  (<PRI>HOST TAG: MSG), PRI = facility*8 + severity; log.host as IP or
  resolved name; config applies live. Messages wait in the queue until
  the interface has an IP. POST /api/log/test sends an info message
  regardless of the level filter.
- Initialised first in app_main so boot messages are captured; the UDP
  socket is created only once the interface is up (creating it before
  esp_netif_init crashed at boot and the bootloader rolled back).
- Verified with a UDP listener: 5424 and 3164 formats, PRI 134/132,
  boot messages delivered after the IP came up, shutdown messages sent
  before reboot, level filter, test message, host by DNS name.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

components/aes67_syslog/include/aes67_syslog.h

@@ -4,5 +4,6 @@
 
 #include "esp_err.h"
 
-// Registers the "log" config group. (Sender itself: step 5.)
+// Registers the "log" config group, hooks esp_log (still printed on the UART) and starts the
+// sender task. Messages logged before the interface has an IP are queued (up to the queue size).
 esp_err_t aes67_syslog_init(void);