No PIN-code fallback path for devices without biometrics enrolled

[ndii-dev]

Any future biometric gate (see the related issue) needs a fallback for devices with no Face ID/Touch ID/fingerprint enrolled, or where the user has disabled biometrics at the OS level — currently there's no PIN system in this app at all to fall back to. Design and implement an app-level PIN as a first-class alternative, not an afterthought, including its own brute-force lockout policy (distinct from OS-level biometric lockout).

Definition of done:

• PIN setup flow during onboarding when biometrics are unavailable
• Lockout/backoff after repeated failed PIN attempts, tuned independently of any biometric lockout
• PIN itself never stored in a form that permits offline brute-forcing if SecureStore's protection is somehow bypassed (e.g. store only a salted hash comparison, not the PIN itself)

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Before opening a PR for this issue, read CONTRIBUTING.md.

This is not a starter-issue. The Definition of done above is the full
acceptance criteria, not a subset to sample from — a PR that addresses part
of it is an unfinished issue, not a smaller one. Your PR must include, in
the PR description itself:

• Root cause / design-decision rationale in your own words — not a restatement of this issue
• Every Definition of done bullet above addressed explicitly, with a one-line note on how
• Evidence the code actually runs: pasted test/build output, a screen recording or before/after screenshots for UI changes, or real (non-mocked) logs for network/contract-facing work
• New or updated tests included and shown passing (paste the output)
• Any adjacent/related behavior this issue calls out re-verified, not assumed unaffected

PRs missing these will be sent back before review, not reviewed and rejected — please do this up front.

[Ayinkx]

Hi i would like to work on this issue please assign to me
I can do it perfectly

[grantfox-oss]

🦊 GrantFox — @Ayinkx1 has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #28)
2. Your PR will be reviewed by the Orbit-Wal maintainers

Good luck! Track your progress on GrantFox.