AgentWatcher: download ældre versioner

Security
- The installation folder is no longer writable by standard users. Previous
versions granted Full Control over C:\Program Files\Convectiva\AgentWatcher
to the Users group, which allowed any local user to replace the executable
or the helper scripts. Upgrading also removes that permission from existing
installations.
- The PBX API client secret is no longer passed on the PowerShell command
line, where it was visible to other processes and recorded by endpoint
security and PowerShell logging.
- The client secret stored in the registry is now protected with DPAPI.
- Logs moved from the installation folder to %LOCALAPPDATA%\AgentWatcher.

Fixed
- Silent installation (/VERYSILENT, used by "winget install --silent") failed
with exit code 7. The .NET 6 check read the wrong registry view, so the
prerequisite was reported as missing even when installed, and the download
page cannot be shown without a wizard.

Added
- Extension presence can be changed from the tray menu.
- Queues the extension belongs to are listed in the tray menu, with
individual pause and resume.
- Scheduled pauses per queue, with days of the week. A pause starts even if
the screen is locked; the resume waits until the computer is unlocked.