feat: migrate backend from sqlite3 to better-sqlite3

[hadv]

Summary

Migrate the backend database layer from sqlite3 to better-sqlite3 for improved performance and simpler API.

Changes

backend/package.json

• Replaced sqlite3 with better-sqlite3 (v12.5.0)

backend/database.js

• Import: Changed from sqlite3 to better-sqlite3
• Database initialization: Converted from async callbacks/promises to synchronous API
• Pragmas: Now use db.pragma() instead of promise-wrapped db.run()
• Helper functions: Replaced runAsync/getAsync/allAsync with synchronous run/get/all using prepared statements
• All exported functions: Converted from async function to regular function
• Transaction handling: Used better-sqlite3's native transaction API (db.transaction()) for atomic operations in activateDevice()
• Backup: Changed from VACUUM INTO to better-sqlite3's db.backup() API
• Close: Changed from callback-based to synchronous db.close()
• Graceful shutdown: Converted from async to sync

Benefits

Aspect	sqlite3	better-sqlite3
API	Async (callback/Promise)	Synchronous
Performance	Slower due to async overhead	2-10x faster for typical workloads
Simplicity	More complex with callbacks	Cleaner, simpler code
Transactions	Complex to handle properly	Easy: db.transaction(() => {...})()
Native builds	Often problematic	Generally more reliable
Maintenance	Less actively maintained	Actively maintained

Testing

• Backend server starts successfully
• Database initialization works
• FIDO MDS cache loads and refreshes correctly
• Graceful shutdown works properly
• No diagnostics/lint errors

Related Issue

Closes #170

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Pull Request opened by Augment Code with guidance from the PR author