Fix PIN unlock unusable after cancelling biometric prompt (#151)

[MiMoHo]

Summary

Fixes #151. When both PIN and biometric app lock are enabled, cancelling the biometric prompt drops the user onto the PIN keypad — but the passcode was only ever verified as it was typed, with no submit button and no feedback. Because a wrong digit was never rejected, the user could "type in numbers endlessly" and a correct PIN was effectively unreachable once a wrong digit had been entered.

Changes

• NCPAppLock.kt — when the typed passcode reaches the length of the stored passcode and is still incorrect, the screen now shows the existing "Incorrect code" error and clears the input, instead of silently accepting further digits. The stored passcode length is loaded asynchronously and the check only runs once it is known, so a correct PIN of any length still unlocks on the last digit as before.
• AppLockHelper.kt
  • checkPasscode() no longer falls back to the hardcoded "0000" when the stored passcode cannot be read; it returns false instead, so the lock can never be opened with a default code.
  • Added a small pure helper shouldRejectPasscodeAttempt(input, length) that encapsulates the "is this a completed, wrong attempt" decision so it can be unit-tested without the Android runtime.
• Dialogs.kt — InputPasscodeDialog now filters input with all { it.isDigit() } instead of toIntOrNull() != null. The old check rejected passcodes longer than 9–10 digits because they overflowed Int parsing, even though the field allows up to 16 digits.

Testing

• Added JVM unit tests (AppLockHelperTest) covering empty / incomplete / full-length-wrong / over-length / unreadable-passcode / long-passcode cases. All green.
• Manually verified on an Android 15 emulator (the issue's repro): enable PIN + fingerprint → lock → cancel the fingerprint prompt → the PIN keypad now rejects a wrong code with "Incorrect code" and unlocks with the correct one. Also verified the physical-keyboard input path and the setup dialog still accept a normal PIN.
• ./gradlew testDebugUnitTest passes; lintDebug shows only pre-existing findings (unchanged by this diff).

Note

This contribution was made using AI (Claude). All generated code was proofread and validated by the committer.