Add 'Update Plex Libraries' tray menu option

[beni-ma-ru]

What

Adds an Update Plex Libraries option to the tray icon context menu (shown while Plex is running, below "Restart Plex"). Clicking it asks Plex to scan/update all libraries — the same action as "Update Libraries" in the web UI, and a feature people often miss from running Plex as a regular user app.

How

• New UpdateAllLibraries() operation on the ITrayInteraction WCF contract.
• The service (not the tray) makes the request to http://localhost:32400/library/sections/all/refresh, appending the X-Plex-Token read from the registry via the existing PlexRegistryHelper when available. Doing it service-side means the request always originates from the machine hosting Plex, so it also works when the tray app is connected to a remote service instance.
• The request runs in a background task (same pattern as Start()/Stop()) so the tray's short WCF send timeout isn't at risk; the outcome is written to the service log.
• The tray shows a "Library update requested" balloon tip after invoking the operation.

Testing

Tested on Windows 11 against a live Plex Media Server 1.43.2 installation running under PmsService:

• Verified the server rejects the refresh call without a token (401) and accepts it with the registry token (200), confirming the token handling is required and correct.
• Deployed the rebuilt binaries over an existing 1.2.3 install; service started and restarted Plex normally.
• Invoked UpdateAllLibraries() over the WCF channel and confirmed the service log shows Update of all libraries requested, plex responded: OK, with the library scan visible in the Plex dashboard.
• Verified from the tray menu itself: removed a media item from a library folder, clicked Update Plex Libraries, and watched it disappear from Plex; added the file back, updated again, and it reappeared.