feat: Add "Start minimized", "Start at login" options. Use single instance of application.

[awkure]

Summary

This branch improves how Mouser starts: optional tray-only launch from config, cross-platform “start at login” via core.startup, and a Qt local-socket single-instance guard that brings the existing window forward when a second launch is attempted.

Changes

• core/startup.py — New module that applies login startup on Windows (HKCU Run) and macOS (LaunchAgent plist + launchctl), with helpers to build the stored command line for frozen and script runs.
• core/config.py — Version 5 migration now maps legacy start_with_windows only when that key exists, defaults start_at_login otherwise, and removes the old key after migration.
• ui/backend.py — Replaces the previous autostart integration with core.startup: sync on init when supported, clear start_at_login when unsupported, and call apply_login_startup when the user toggles the setting.
• ui/qml/ScrollPage.qml — Copy and layout tweaks: “start at login” row hidden when unsupported; “start minimized” is independent of login and always available; improved wrapping for the description text.
• main_qml.py — Reads start_minimized (and --start-hidden) to set launchHidden; adds QLocalServer/QLocalSocket single-instance logic with activation message to show the main window; optional tray balloon when starting minimized with a system tray.
• Tests — tests/test_startup.py for the new module; tests/test_single_instance.py for instance helpers; updates to tests/test_config.py, tests/test_backend.py, and a small path assertion fix in tests/test_autostart.py.

How to verify

• Run unit tests: python -m unittest tests.test_startup tests.test_config tests.test_backend tests.test_single_instance tests.test_autostart.
• Launch the app twice: the second process should exit and the first should show the settings window.
• With “start minimized” on, first launch should keep the main window hidden (per existing QML) and show the tray hint when a tray is available.

Notes

• Legacy core.autostart remains for existing macOS-specific helpers/tests; runtime login registration is handled by core.startup.

[TomBadash]

Thanks for this great contribution @awkure! Really nice work on the single-instance guard, cross-platform login startup, and decoupling start minimized from start at login.

I made a couple of small fixes before merging:

1. Fixed start_minimized default in main_qml.py — cfg_settings.get('start_minimized', True) was defaulting to True, which would hide the app window on first launch if the config key was missing. Changed to False.

2. Added error handling around �pply_login_startup() in �ackend.py — wrapped in try/except so a registry or launchctl failure emits a status message instead of crashing.

3. Fixed est_autostart.py — str(Path(fake_executable)) converted forward slashes to backslashes on Windows, breaking the assertion. Reverted to direct string comparison.

4. Resolved merge conflicts with master (config migration v6, import merges, test version assertions).

All tests passing. Merging now!