feat(housewallet): port the cu-04b house wallet screen

[netqo]

Summary

Ports the cu-04b operator house wallet screen (mockup/js/screens/house-wallet.js) and wires it into the nav graph in place of the placeholder. All five mockup states are covered: Generate / Import setup, the active wallet (balance, public address, Android-Keystore-backed private key), the key-revealed view with an auto-hide countdown, the biometric prompt overlay, and the no-biometric error (preview-only).

This branch also lands two pieces the screen depends on, each in its own commit:

• refactor(util): truncateMiddle (the middle-ellipsis shortener) moves from feature/rounddetail to util/ so the provably-fair seeds and the house wallet address share it.
• feat(ui): an in-app toast host styled like mockup/js/toast.js (success / error / info / warn), hoisted in StackApp and reachable from any screen via LocalToastController.

Rationale

• No ViewModel (KISS): wallet existence, key-revealed and prompt visibility are screen-local state; Generate / Import create the wallet, "Reveal with Biometric" raises the prompt, authenticating reveals the key (auto-hiding after a countdown), Hide Now re-masks it.
• The public address renders on a single line, middle-truncated (first 10 + last 8), with spacing between the field and the copy / Polygonscan chips so they no longer collide (addresses earlier review feedback).
• The chip actions are functional with the standard ripple: refresh and copy confirm via the in-app toast (copy also writes the full address to the clipboard); Polygonscan opens the explorer, toasting on failure.
• Real key generation / import, the Android Keystore and the on-chain balance arrive with the wallet repository; the review-less states are preview-only.

Verification

• ./gradlew ktlintCheck detekt testDebugUnitTest -> BUILD SUCCESSFUL
• ./gradlew assembleDebug -> BUILD SUCCESSFUL
• ./gradlew compileDebugAndroidTestKotlin -> BUILD SUCCESSFUL
• On device: Profile -> House Wallet runs the full flow (setup, reveal with the biometric overlay + countdown, hide), the address is single-line, and the three chips fire their toasts.

Test plan

• ktlint + detekt clean
• HouseWalletFormatTest and TruncateMiddleTest green
• HouseWalletScreenTest compiles (instrumented; not run in the CI matrix)
• Debug APK assembles
• Manual device walkthrough

Checklist

• Commit messages follow Conventional Commits (see CONTRIBUTING.md).
• Branch name follows the naming convention (feat/).
• The change is scoped: house wallet plus the two helpers it needs (each its own commit).
• If user-visible behavior changed, CHANGELOG.md has been updated under [Unreleased].
• If a new dependency was added, it is justified in the PR description. (No new dependency.)