style: clear whitespace, unused-import and blank-line lint

Strip trailing whitespace, drop unused imports/variables/global statements,
split multi-imports, fix E3xx/E1xx spacing and E712 comparisons. No behaviour
change; only E501 long lines remain in flake8.

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

hbd/server/cli.py

@@ -120,7 +120,7 @@ def cmd_passwd(args):
 def cmd_notify(args):
     """Send a test message via a single notification channel."""
     from .config import load_config
-    from .notify import Notification, _dispatch_to_channel, setup
+    from .notify import Notification, setup
 
     config = load_config(args.configfile)
     setup(config)
@@ -193,7 +193,9 @@ def _read_pid(configfile) -> int | None:
 
 
 def cmd_stop(args):
-    import os, signal as _signal, time
+    import os
+    import signal as _signal
+    import time
     pid = _read_pid(args.configfile)
     if pid is None:
         sys.exit(1)
@@ -212,7 +214,8 @@ def cmd_stop(args):
 
 
 def cmd_reload(args):
-    import os, signal as _signal
+    import os
+    import signal as _signal
     pid = _read_pid(args.configfile)
     if pid is None:
         sys.exit(1)
@@ -222,7 +225,10 @@ def cmd_reload(args):
 
 
 def cmd_restart(args):
-    import os, signal as _signal, time, subprocess
+    import os
+    import signal as _signal
+    import time
+    import subprocess
     pid = _read_pid(args.configfile)
     if pid is not None:
         print(f"Stopping hbd (pid {pid})...")