feat(zap): move instant-zap config into the zap sheet's Edit Presets

[dmnyc]

Summary

Instant-zap setup was buried in Settings → Interface, easy to miss. Move it into the zap sheet — where it's actually used.

• ZapSheet instant-zap row — when enabled, shows the configured amount + message and a "configure in Presets" caption; the bolt icon tints accent when on.
• EditPresetsSheet — adds an "Instant zaps" toggle ("Instant payments" in fiat mode) with the caption "Long-press the bolt to send the selected preset instantly," plus a per-preset leading selector (checkmark.circle.fill / circle) enabled only while the toggle is on. Done persists quickZapEnabled + the selected preset's amount (clamped 1–10,000 sats) and message. Deleting the selected row reselects the first.
• InterfaceSettingsView — the instant-zap block is removed. The Currency (fiat mode) section is untouched.

Fiat mode is unaffected — it stays in Settings as an app-wide units toggle. Default stays off; long-press instant zap fires the configured amount, unchanged.

Scope notes

• The amount hint in the sheet shows sats even in fiat mode (matches the Android reference).
• Presets are sats-based, so Edit Presets only sets the sats instant amount. In fiat mode an instant zap still fires the last-saved fiat value (quickZapAmountFiat), which is no longer editable in this UI. Fiat-mode instant-zap handling will be addressed in a follow-up — out of scope here.
• Instant-zap settings remain device-local, per account. NIP-78 cross-device sync stays deferred — tracked in Persist user settings with NIP-78 #70.

Screenshots

Zap sheet — instant row	Edit Presets — selection	Settings — block removed
Instant-zaps toggle shows amount + message + "configure in Presets"	Leading selector picks the instant preset	Interface settings no longer has the instant-zap block

Test plan

• Build succeeds, installed and ran on simulator
• Zap sheet: instant-zaps toggle shows amount + message + "configure in Presets" when on; bolt tints accent
• Edit Presets: toggle + per-row selection; Done persists enabled + selected preset's amount & message; the sheet reflects it
• Deleting the selected preset row reselects the first row
• Settings → Interface: instant-zap block gone; Fiat mode intact
• Long-press a post's zap button fires the configured instant amount
• Default off on a fresh account; switching accounts swaps presets + instant selection

Follow-up

• Fiat-mode instant zaps — let Edit Presets set the fiat instant amount too (or derive it from the selected preset), so fiat users aren't stuck on the last-saved value. Deferred to a follow-up.
• Android design parity — spec written to align dark-wisp / wisp-Android with this layout (leading selector, cleaner header, airier rows); ported separately.