Passcode Lock Screen

This is already supported in the mobile app versions.

### What
Passcode settings where you enable and set code (can use fingerprint if supported by OS) and when to lock - immediately, after 1 min or after 10 min, etc.

### Why
For privacy reasons. By requiring a passcode, we can ensure that our notes are kept private and are not visible to others who may use the same device.

### How
A user can enable this from the settings screen. I'm attaching the same feature from the Telegram desktop app.

Click to see screenshots of Telegram

Passcode | Auto-lock settings expanded
:-------------------------:|:-------------------------:
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Start by reviewing the existing settings screen and the mobile app implementations referenced in the issue, then compare the attached Telegram passcode and auto-lock behavior. Done means users can enable and set a passcode, use supported OS fingerprint authentication, choose an auto-lock interval, and keep notes inaccessible until unlocking.

Written by the indexing model from the issue text.