fix: debounce clicks and deduplicate scans

[ovitrif]

Fixes #831

This PR:

1. Adds click debouncing across all interactive UI elements to prevent accidental double-taps
2. Ensures only one scan job runs at a time, deduplicating concurrent scan inputs from paste, scanner, deep links, and address entry

Description

Rapid taps on clickable elements (buttons, navigation icons, tabbar buttons, drawer items, overlays, etc) could trigger duplicate actions (double navigations, duplicate payments, etc.). A ClickDebouncer utility with a 500ms window is added and exposed as rememberDebouncedClick. All interactive surfaces now route through debounced click handlers.

The scan deduplication consolidates four separate handleScan() call sites into a single launchScan() method that tracks the active scan job and input, cancelling prior scans when a new one arrives and skipping exact duplicates.

Preview

Before	Multi Clicks	Multi Paste
before.mp4	multiClicks.mp4	multiPaste.mp4

QA Notes

1. Button debouncing

1. Open the app and navigate to any screen with buttons (e.g. Send, Receive, Settings)
2. Rapidly multi-tap on any button
3. Verify only one action is triggered (no duplicate actions)

2. Navigation debouncing

1. Tap the back arrow or any navigation components rapidly (ie. Settings clickables)
2. Verify no double navigation occurs

3. Tabbar buttons and drawer items

1. Rapidly tap between bottom tabbar buttons
2. Open the drawer and fast multi tap menu items
3. Verify smooth single-action behavior

4. Scan deduplication - bug: #831

1. Enable QuickPay & copy a LN invoice with amount below treshold
2. Rapidly multi tap Paste buttons on scanner or Send sheet
3. Verify only one scan processes (check logs for "Skipping duplicate scan")
4. Verify scan and quickpay proceeds without issues

5. Overlay and sheet dismissal

1. Tap the scrim/overlay area of a bottom sheet rapidly
2. Verify it dismisses once without flicker

[jvsena42]

Found this bug when double tapping the NumberPad

Screen_recording_20260311_143238.webm

[ovitrif]

Fixed the NumberPad double-tap issue in 32711b8 — added a debounce parameter to clickableAlpha (defaults to 500ms) and set debounce = Duration.ZERO on NumberPad keys so rapid presses aren't swallowed.

Preview

fix.mp4

[ovitrif]

Addressed both review comments in fb7168a:

• ClickableAlpha.kt: Added else branch to restore alpha to 1f when tap is debounced
• AppViewModel.kt: Log message now starts with verb: "Starting scan from ..."

needs re-review