refactor: remove dyndnshosts/drophosts legacy config keys, fix DNS event logging

- Remove dyndnshosts legacy list; dyndns is now set per-host in the hosts section
- Remove drophosts config key and load-time deletion loop
- Simplify get_dyndnshosts() to only read per-host dyndns attributes
- Fix dns_update_worker to call eventlog with correct (host, level, msg) signature
- Log INFO/ERROR events per domain on each DNS update instead of one batched message
- Add logger to dns.py (was missing, causing NameError on update failure)
- Update README and tests to reflect removed config keys

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

hbd/server/main.py

@@ -78,9 +78,7 @@ async def reload_configuration(config_obj, config_path, components):
         True if reload succeeded, False otherwise
     """
     try:
-        logger.info("=" * 60)
         logger.info("Starting configuration reload...")
-        logger.info("=" * 60)
         
         # Reload config file
         new_config = await config_obj.reload(config_path)
@@ -115,13 +113,11 @@ async def reload_configuration(config_obj, config_path, components):
         # These are reloadable and effective immediately:
         # - notification_channels
         # - threshold_configs
-        # - hosts (watchhosts, dyndnshosts, notification_channels)
+        # - hosts (watchhosts, dyndns, notification_channels)
         # - grace period (used on next heartbeat)
         # - debug/verbose flags (used on next message)
         
-        logger.info("=" * 60)
         logger.info("Configuration reload completed successfully")
-        logger.info("=" * 60)
         return True
         
     except Exception as e:
@@ -422,7 +418,6 @@ def load_pickled_hosts(config, hbdclass):
     pickfile = config.get("pickfile", "hbd.pickle")
     dyndnshosts = config_mod.get_dyndnshosts(config)
     watchhosts = config_mod.get_watchhosts(config)
-    drophosts = config.get("drophosts", [])
     if 1 and os.path.exists(pickfile):
         if config.get("verbose", False):
             logger.info("opening pickls %s", pickfile)
@@ -448,9 +443,6 @@ def load_pickled_hosts(config, hbdclass):
             hbdclass.Host.hosts[h].apply_access(
                 access["owner"], access["managers"], access["monitors"]
             )
-        for h in drophosts:
-            if h in hbdclass.Host.hosts:
-                del hbdclass.Host.hosts[h]
         if config.get("verbose", False):
             logger.info("%s pickled hosts loaded", len(hbdclass.Host.hosts))
     else: