feat(fees): working network fee selection for sell and pay

[BullishNode]

⚠️ Requires emulator/device review before merge — draft until verified. Test: on a bitcoin-wallet sell (and pay), tapping "Network fee priority" opens the fee dialog; the row shows the actual selection; the summary network fee updates with the choice; and ideally one real staging sell at economy/custom rate confirming the broadcast transaction pays the selected sat/vB. This is the money path — the riskiest PR of the set.

Stacked on #2535 (fix/sell-hardening) — review only the last commit. After #2535 merges, this retargets to main. Must merge AFTER #2534 (pay-status PR): that branch constructs sendPaymentConfirmed event params this PR removes — the rebase reconciles two one-line call sites (pay_send_payment_screen.dart, test/features/pay/pay_bloc_test.dart), already verified on the integration branch.

Problem (#2521)

The "Network fee priority" row on sell and pay confirmation screens was a debugPrint stub with a // TODO; every transaction paid the fastest rate end-to-end — the bloc ignored the fee selection its confirm event already declared.

Changes

• SellBloc/PayBloc implement the shared fee modal's FeeModalViewState/FeeModalActions ports, following SendCubit semantics: presets, custom sat/vB or absolute fees with arm/disarm/finalize, epoch-guarded previews, relay-floor gate
• The row opens the shared FeeOptionsModal and displays the committed selection; the summary fee reprices from a real PSBT built at the selected rate
• Confirm prepares/signs/broadcasts at the committed selection. Unlike send/swap, preview PSBTs are display-only: sell/pay rebuild at broadcast time because a price-lock refresh can move the order's payin amount. The built fee is re-asserted against the relay floor before signing
• Fee editing locks while confirming or once the payin is broadcast; every post-await emit merges into live state — a recalculation or preview landing after the flow moved on emits nothing (reviewer-caught blocker, regression-tested in both blocs)
• Previews price against the order's real payin address; Liquid payins keep no fee row

Validation

Sell suite 13/13, pay suite 8/8 (selected-preset-reaches-prepare, custom-fee path, below-floor rollback, events-inert-once-latched, preset previews, post-success recalc emits nothing — the money-path tests capture every networkFee handed to prepare and assert it equals the picked tier); analyze clean; reviewed with a verification pass (1 blocker + 2 should-fixes applied).

Closes #2521