[MediaMarco]

Summary

Makes the location of the accounts file configurable and adds a tray menu to switch between recently used accounts files.

Configurable accounts file

• New accounts_path option in ~/.logsmith/config.yaml, e.g. accounts_path: ~/some/dir/my-accounts.yaml
• The file name can be anything, but it must have a .yaml or .yml extension
• ~ and environment variables (e.g. $HOME) are expanded
• An invalid extension shows a config error and falls back to the default ~/.logsmith/accounts.yaml
• Missing parent directories/files are created on startup and save
• Saving via "Edit config" preserves the setting

Switch accounts file (tray menu)

• New "Switch accounts file" submenu listing the last 10 used accounts files. It only shows files that exist, and the active one is checked
• "Open accounts file..." opens a file picker that only shows .yaml/.yml files
• Switching logs out, persists accounts_path and accounts_path_history to config.yaml, reloads the profile groups and rebuilds the tray menu

Fix

• app.setQuitOnLastWindowClosed(False): Closing the file picker caused Qt to quit the tray app because it was considered the "last window"

Testing

• Added unit tests for path resolution, extension validation, history handling and Core.switch_accounts_file
• All 271 tests pass
• Smoke-tested switching via the history menu and the file dialog with Qt offscreen