feat: Implement startup logging to DB

[motionduck]

Changelog:

• Added a startupLog helper and a startupLogs array in env.ts to capture and temporarily store log messages during startup, before the main logger is ready. These logs are later drained and logged using the main logger once initialization is complete.
• In server.ts, after the database connection is established and the main logger is available, all the stored statup logs are drained and logged to the database.
• Specified rootDir in backend tsconfig.json to fix warning in the TypeScript project structure.