Add Keyboard Switcher link in Setting and Onboarding

### Checks

- [x] I have read the Wiki, searched the open issues, and still think this is a new bug.

### Explain the problem clearly and succinctly:

Example flow:
* In some app, at login entry field. DB is locked
* Long press space, switch to Magikeyboard
* Press 🗝️ to open KP
* Unlock DB (with biometric or password)
* Auto selection is made, user is switched to previous app
* Keyboard is default, not Magikeyboard

Notably, it doesn't matter if default keyboard was even needed (e.g. biometric flow

### Describe what you expected to happen:

_No response_

### KeePassDX version:

4.4.0_beta3

### Build:

Free

### Database version:

_No response_

### File provider (`content://` URI)

_No response_

### Android version:

16

### Android device:

Pixel 10 pro xl

### Additional context:

_No response_

Start by reviewing the Settings and onboarding entry points named in the issue, then reproduce the documented login and keyboard-switching flow on Android. Determine where a Keyboard Switcher link should appear in both areas and verify that it remains available after unlocking and returning to the previous app.

Written by the indexing model from the issue text.