fix(tips): match tip card sizing to iOS on the screen and camera

[bmc08gt]

Problem

The tip card rendered at inconsistent sizes. The My Tip Card screen and the scanner/camera each fed TipCard a different width constraint, and the card sized its QR off that constraint (maxWidth * 0.65) — so the two Android surfaces never matched each other, and neither matched iOS. iOS renders the card noticeably smaller/portrait; ours was wider and squarer.

Fix

Port iOS's TipcardView sizing model, where the card width is primary and every inner metric derives from it (matching Flipcash/Core/Screens/Main/Tips/TipcardView.swift):

Metric	Formula
Aspect ratio	1.16 (portrait)
QR / scannable code	0.68 × width (square)
Corner radius	0.08 × width
Avatar	0.09 × width
Name-row top gap	0.06 × height

Per-surface width, matching iOS:

• My Tip Card screen — fixed, device-independent 300dp (iOS TipcardScreen.cardWidth = 300)
• Scanner / camera — min(canvasWidth × 0.82, 320dp) (iOS BillCanvas.tipcardSize)

Threaded via a new cardWidth: Dp? param on TipCard / ScannableRenderer (null → camera formula; the screen pins 300dp).

Result (393dp/pt device)

Surface	iOS card / QR	Android now
My Tip Card screen	300 / 204	300 / 204
Camera	289 / 196	289 / 196

Notes

• Tint opacity is intentionally left as-is (Android camera uses its own frosted-blur / opaque-fallback path); this PR is sizing only.
• The camera keeps its existing BiasAlignment vertical positioning; only the card's interior sizing changed.

Test

• :shared:bills, :features:tipping, :features:scanner, :features:currency-creator compile clean.