Implement Android TOTP and confirmed HOTP presentation (#107)

docs/android/otp.md

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+# Android one-time passwords
+
+Issue [#107](https://git.rfc1437.de/hugo/IronStorage/issues/107) connects the TOTP
+destination to the storage-owned discovery catalog. Opening the list reads cached
+metadata without decrypting entries. Select a row, then Unlock to display its
+issuer, account, grouped code, countdown and progress. Refresh TOTP catalog is an
+explicit authenticated discovery action; the progress/search workflow belongs
+to [#110](https://git.rfc1437.de/hugo/IronStorage/issues/110).
+
+The normal entry viewer and TOTP detail use the same code component and native
+viewer controller. Decryption, creation and editing reconcile the catalog in
+Rust. Only nonsecret row identities and revisions are restored after recreation.
+OTP parameters, codes and authentication secrets are never persisted by Kotlin.
+
+Rust computes SHA1/SHA256/SHA512 codes, six/eight digits, custom periods, absolute
+validity boundaries, grouping and countdown. The composed code component owns a
+STARTED-lifecycle coroutine that submits OS clock facts without touching the
+authentication lease. Scrolling it out or leaving stops decryption/countdown ticks;
+an expiry-only native window check still erases held codes when hidden. Rust validates each
+returned window before publication, including delayed results and backward clock
+changes. Lock, background, expiry, entry changes and stale revisions remove codes
+and cancel presentation. Explicit copies use the existing sensitive clipboard
+adapter and Rust timeout/ownership checks.
+
+HOTP in the normal entry viewer requires Generate next HOTP code and a separate
+counter confirmation. The existing pass-otp core increments and atomically commits
+the encrypted counter before returning its code. Refresh and Copy use that same
+committed counter without incrementing. Stale documents, open editors, failed Git
+commits and overflow cannot consume a counter. The TOTP discovery catalog remains
+specific to time-based entries. Android exposes no Watch sharing controls.
+
+## Validation
+
+Rust tests cover RFC 6238 algorithm vectors, six/eight digits, 30/60-second
+boundaries, cache agreement, polling without lease renewal, malformed URI
+diagnostics, stale revision revocation, HOTP confirmation, copy/refresh stability,
+commit rollback and counter overflow. Android's NativeOtpPresentationTest uses
+real encrypted stores with fake wall/lease clocks to verify catalog-only reads,
+boundary transitions, tick lease expiry, clipboard handoff expiry, queued user
+actions overtaking read-only observations, both HOTP generations and background
+revocation. TotpScreenTest covers explicit unlock, grouped code/countdown/copy,
+lock cleanup, HOTP confirm/cancel, tick cancellation on leaving and 300% text
+without clipped digits. Computer use inspects the same Compose
+components on an ARM64 emulator using disposable presentation fixtures.
+
+All emulator installs preserve the retained app container. Production Keystore
+and biometric enrollment are unchanged by this story; the native controller tests
+provide deterministic OS capability callbacks. Supported release ABIs remain
+arm64-v8a and armeabi-v7a; physical devices and x86_64 are outside this milestone.