Improve hotkey capture and notification settings

[phoenixray2000]

Summary

• Add visible hotkey-capture feedback, clear/escape behavior, and robust Alt/Alt+Shift hotkey capture during settings edits.
• Add settings to reuse the start-recording hotkey to stop active recordings and to enable/disable tray notifications.
• Preserve legacy dedicated stop-hotkey behavior, update README docs, and add regression coverage for hotkey capture, settings migration, tray notifications, and record-hotkey stop behavior.
• On Windows, run recording hotkeys through an app-owned low-level keyboard hook so mapped/injected shortcuts such as Caps+r -> Alt+Shift+R can trigger recording reliably.

Root cause

Qt could miss Alt-based letter events during settings capture, so capture needed a temporary keyboard hook. A later runtime issue came from the trigger side: keyboard.add_hotkey() can miss AHK-injected Alt combinations, and RegisterHotKey was not reliable for the reported shortcut because Alt+Shift+R is already registered on this machine (ERROR_HOTKEY_ALREADY_REGISTERED, 1409). The runtime path now uses a low-level Windows hook for parsed hotkeys and keeps keyboard only as a fallback for unsupported shortcut strings.

Impact

Users can configure Alt/Alt+Shift shortcuts reliably, see when the app is waiting for a shortcut, stop recording with the same start shortcut when enabled, choose whether tray popup notifications are shown, and trigger configured recording hotkeys through Caps-layer mappings.

Validation

• .\\.venv\\Scripts\\python.exe -B -m unittest discover -s tests -v -> 26 tests passed
• .\\.venv\\Scripts\\python.exe -m compileall -q main.py gui.py audio_recorder.py clipboard_utils.py tests -> passed
• .\\.venv\\Scripts\\python.exe -c "import main; print('import main ok')" -> passed
• PyInstaller packaging succeeded
• Latest packaged artifact: dist\\QuickAudioRecorder.exe

[phoenixray2000]

Latest update has been tested locally with the Caps-layer mapping case. The PR is mergeable and ready from my side; upstream maintainer permission is required to merge.