feat(wallet): iOS-parity Receive screen — text input + note + invoice / address tabs

[dmnyc]

Summary

Ports the iOS ReceiveInvoiceSheet layout to Android. The orange numpad-style Receive screen is replaced with a form: amount text field, optional note field, and a Create invoice CTA. When the user has a Spark lightning address, an Invoice / Lightning Address segmented control appears at the top and the address tab renders the QR + Copy / Share row inline.

Before / After:

iOS (target)	Android (this PR)
Form: AMOUNT + NOTE + Create invoice	Same layout, Material 3 components, surface variant rounded fields

Changes

• WalletScreen.kt
  • Rewrites ReceiveAmountContent from a SatsNumpad driver to a BasicTextField-based form: AMOUNT field (numeric keyboard, "0" placeholder, "sats" or fiat suffix), NOTE field (placeholder "For coffee, etc."), Create invoice button.
  • In fiat mode, live sats conversion is shown below the amount.
  • Adds optional Invoice / Lightning Address SingleChoiceSegmentedButtonRow at the top — only rendered when walletViewModel.lightningAddress is non-blank.
  • Adds ReceiveAddressBlock composable: QR card with the address centered below + Copy / Share row beneath. Reuses the same QR generation path as LightningAddressQRContent.
• WalletViewModel.kt
  • generateInvoice now takes (amountSats: Long, description: String = "") and passes the description to WalletProvider.makeInvoice. The description ends up in the BOLT11 invoice memo.
  • Adds setReceiveAmount(value: String) for the new text-input path. The old updateReceiveAmount(digit) / receiveAmountBackspace() setters stay untouched since the Send flow still uses them.
• values/strings.xml — new English strings:
  • wallet_receive_invoice_tab = "Invoice"
  • wallet_receive_address_tab = "Lightning Address"
  • wallet_receive_amount_label = "AMOUNT"
  • wallet_receive_note_label = "NOTE (OPTIONAL)"
  • wallet_receive_note_placeholder = "For coffee, etc."
  • wallet_receive_create_invoice = "Create invoice"
  • Translations to follow in a separate PR.

What's NOT in this PR

• Deposit max cap: amounts above the wallet's max receive still fail at backend invoice creation. Tracked in Wallet: cap deposit / invoice amount with sensible max #577 (Android) / Wallet: cap deposit / invoice amount + show amount above QR on Receive wisp-ios#209 (iOS) — pick one cap number for both platforms.
• The Wallet TopAppBar still says "Wallet" with a back arrow (Android scaffold pattern) instead of the iOS modal "Receive" + Close-pill chrome. Body shows "Receive" header underneath. Happy to revisit if we want a stronger modal feel.

Test plan

• Build (./gradlew assembleDebug) on clean main base
• Device tested on R5CW60D6EJF — design approved
• Invoice creation succeeds with and without note (note appears in BOLT11 memo)
• Fiat mode shows "≈ N sats" supporting line and creates invoice with the converted sats amount
• Segmented control appears only when a lightning address is set up; switching tabs shows the address QR + Copy / Share inline
• Create invoice button is disabled (gray) when amount is empty or zero

Reference

iOS: wisp-ios/WalletView.swift → ReceiveInvoiceSheet (~lines 984–1230)