feat(ui): frosted liquid-glass app-bar chrome + currency-info

[bmc08gt]

Summary

Adds an opt-in Haze "liquid glass" frost to the app-bar action chrome and wires the v2 currency-info screen to it — so content scrolls under the back button, title pill, and share button as frosted glass (Apple-Wallet style), matching the iOS reference. This also replaces the currency-info screen's heavy top fade with the chat-screen's soft bg→transparent scrim.

Stacked on #1247 (the currency-info layout PR) — review/merge that first.

Reusable plumbing (ui/components)

• CircularIconButton gains an optional hazeState → frosts whatever scrolls beneath the bar (clip precedes hazeEffect so the blur is bounded to the circle); flat translucent fill when null.
• AppBarDefaults.UpNavigation / Close / Share and AppBarWithTitle thread the optional hazeState. Fully backward-compatible (default null = today's look).

Currency-info (features/tokens)

• Chat-style overlay: content fills behind the app bar (marked as the haze source), inset below it by the measured bar height, with a bg→transparent scrim for the soft top fade. Replaces the CodeScaffold + drawn scroll-gradient.
• Back/share buttons and the scroll-revealed title pill are frosted glass over the content.
• Adds the haze bundle to :features:tokens.

Verified on device

Dad Cash: at rest the card sits below clean frosted chrome (no pill); scrolling reveals the frosted "Dad Cash $20,673.39" pill and the card glides under the glass — no heavy fade. Matches the reference.

Note

This also resolves the "fade too aggressive" feedback on #1247. If preferred, the currency-info visual half can be folded into #1247 and this PR kept to just the reusable CircularIconButton/AppBar plumbing — flagged for review.