Fix potential app hang during startup after v0.8.0 update

[hjiangsu]

Pull Request Description

This PR fixes an issue where a partial database migration (possibly caused by a version upgrade) could cause Thunder to hang on the splash screen. The following changes were made:

• Improved database migration handling: When adding new columns to existing tables, the migration process now checks whether the column already exists before attempting to add it.
• Added a database integrity check on startup: This ensures that the platform field under Accounts is properly initialized. This field is required to distinguish between PieFed and Lemmy accounts.
• Updated splash screen behavior: The splash screen no longer waits for app initialization to complete before disappearing. This prevents certain error messages from being hidden during startup.

I've also bumped the version here as there was some testing done!

Issue Being Fixed

Issue Number: Issue mentioned in the Matrix channel

Screenshots / Recordings

Checklist

• If a new package was added, did you ensure it uses an appropriate license and is actively maintained?
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