V16/firstboot onstartup conflict fix

[KevinJump]

Fixes an issue with FirstBoot, where content isn't published at the end (like it is with ImportAtStartup)

• FirstBoot runs in a migration and is now UnScoped so we can control the context like we do for the ImportAtstartup version, so they both work the same.
• Added a Check to the uSync StartupImportAsync method so it generats a hash of the passed in parameters and will only run that import once. This means if firstboot and importonStartup are importing the same things - it only runs once, but if they are different they will both run.
• the call in ImportOnStartup was StartupImportAsync(...).Wait() when its in an async method so it can be async StartupImportAsync(...)

[Copilot]

Pull Request Overview

This PR fixes a conflict issue between FirstBoot and ImportAtStartup functionality in uSync, ensuring content is properly published during FirstBoot operations and preventing duplicate imports when both features use the same parameters.

Key changes:

• Added deduplication logic to prevent duplicate startup imports with identical parameters
• Converted FirstBoot to use UnScoped migration pattern with proper context management
• Fixed async/await pattern in ImportOnStartup notification handler

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
SyncService.cs	Added hash-based deduplication for startup imports to prevent conflicts
uSyncApplicationStartingHandler.cs	Fixed async/await pattern by removing .Wait() call
FirstBootMigration.cs	Converted to UnScoped migration with proper context management and server role checks

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