fix: Add validation for corrupted database cache and downloads

[ConsciousEnergy]

This PR adds robust validation to prevent and recover from corrupted database cache scenarios.

Problem:
When the database file is missing or corrupted, the app would cache HTML error pages (404 responses)
in IndexedDB, leading to "file is not a database" errors on subsequent loads.

Solution:

• Validates cached data before use (size >100MB + SQLite magic bytes check)
• Validates downloaded data before caching
• Detects HTML error pages early via content-type checking
• Automatically clears corrupted cache and triggers fresh download
• Provides clear error messages with download instructions

Related Issues:

• Fixes Error: no such table: ElementPropertiesPlus #53 (partial - addresses root cause of corrupted cache)

Testing:

• ✅ Verified corrupted cache is detected and cleared
• ✅ Verified fresh download works correctly
• ✅ Verified validation prevents invalid data caching

Files Changed:

• src/services/database.ts - Added validation logic
• src/services/dbCache.ts - Cleaned up debug logs
• src/services/queryService.ts - Minor cleanup

[bryanchriswhite]

Thanks again @ConsciousEnergy for stepping up! ❤️‍🔥

As I was reviewing #53, I realized that I did make some changes in this direction already, but after discussing it with Claude, it seems like left some room for improvement, and the changes you propose include some additional improvements still.

Here's the convo I had with Claude: