fix: qr code decoding error message

[jvsena42]

Fixes #502

This PR updates the error message shown when pasting or entering unrecognized data to match the iOS behavior. Previously, Android showed "Decoding Error" / "Unable To Interpret Provided Data" while iOS shows "Unable To Read QR" / "Bitkit is not able to read this QR code."

Description

Changes the toast message for unhandled scan data in AppViewModel from other__scan_err_decoding / other__scan_err_interpret_title to other__qr_error_header / other__qr_error_text, aligning Android with iOS parity.

Preview

Screen_recording_20260203_135846.webm

QA Notes

1. Paste invalid data

1. Copy random text (not a valid address, invoice, or LNURL)
2. Navigate to the Send screen
3. Paste the text into the recipient field
4. Verify toast shows "Unable To Read QR" with description "Bitkit is not able to read this QR code."

2. Enter invalid data manually

1. Navigate to the Send screen
2. Type random characters into the recipient field
3. Tap the continue/paste button
4. Verify same error message appears

3. Regression - Valid inputs still work

1. Paste a valid Bitcoin address - should proceed normally
2. Paste a valid Lightning invoice - should proceed normally
3. Scan a valid QR code - should proceed normally

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.