Update bluetooth.py: fix import crash; add robust no-BT fallback

[pullclone]

This commit fixes an import-time crash in bluetooth.py and makes the agent robust when DBus/GLib bindings or the BlueZ daemon are missing.

• Pass human-readable message as the first arg and DBus error name via name= (e.g., org.bluez.Error.Rejected, org.bluez.Error.Canceled).
• Switch Agent capability to KeyboardDisplay so both PIN and passkey flows are supported.

Robust behavior when Bluetooth is unavailable

• Introduce HYPERPANEL_BT_KEEP_ALIVE env flag (default: off).
  • When deps or BlueZ are missing, either exit(0) or idle (GLib loop/sleep) based on the flag.
• Add helpers:
  • idle_or_exit to centralize graceful shutdown/idle behavior.
  • is_bluez_running to check org.bluez on the system bus before attempting registration.
• Improve user interaction and notifications:
  • request_input_sync uses zenity when available, otherwise falls back to TTY input; handles cancellations cleanly.
  • send_notification_with_actions returns a Callable[[], None] disconnect and safely unregisters signal handlers; logs and no-ops if notifications aren’t available.

Other additions

• More informative logging around agent registration and user prompts.
• Defensive handling when removing signal receivers.
• Typing polish for send_notification_with_actions.

Behavioral notes

• No behavioral change when BlueZ and deps are present: the agent registers and runs the GLib main loop as before.
• When BlueZ or deps are missing, hyprpanel no longer aborts due to a parse error; the script exits 0 by default unless keep-alive is requested.

Testing tips

• Catch syntax errors early: python3 -m compileall -q /usr/share/hyprpanel/scripts/bluetooth.py
• Simulate missing BlueZ: systemctl stop bluetooth; run the script and verify exit code 0 (or idle when HYPERPANEL_BT_KEEP_ALIVE=1).
• Start hyprpanel and confirm it no longer aborts on bluetooth.py