feat(recovery): make on-chain sweep work on mainnet, add ASP switching

[Jeezman]

Recovery / unilateral-exit sweep.

The SDK's send_on_chain builds a 0-fee transaction the relay rejects "min relay fee not met"), so sweeping unilaterally-exited VTXOs never worked on mainnet. Replaced with a self-built, fee-bearing sweep:

• build_sweep_tx: copy ark-core's proven taproot script-path build/sign sequence but reserve a real fee from change (sweep_fee, sized from the live fee rate; floored at 1 sat/vB).
• Discover sweepable outpoints from the cached candidates the UI shows (not a gap-limit address scan, which missed unrolled VTXOs); resolve scripts via the connected client's authoritative get_offchain_addresses, reconstructing default VTXOs only as an offline fallback.
• Select all mature inputs and clamp the sent amount to selected − fee, so a near-max ("Max") sweep sends total − fee instead of failing when the fee exceeds a fixed headroom.
• Unify VTXO/boarding maturity on can_be_claimed_unilaterally_by_owner with a 2h MTP safety margin so a near-boundary sweep isn't built non-final.
• Resolve owner keys via the live provider's get_keypair_for_pk (no fixed derivation ceiling when connected).
• Surface fee-estimate failures instead of broadcasting at relay-minimum; get_fee_rate falls back to the nearest target, not 1.0 sat/vB.

ASP switching

• probe_asp / switch_asp commands: validate + test-connect, hard-block a network mismatch (sourced from wallet.json, refusing when unknown), persist to settings.json + wallet.json, and rebuild the live client in place via reconnect_wallet_client (restart-to-retry on failure).
• AspConfig gains a switch mode (probe → typed confirm) launched from Settings.

Send / Receive UX

• Shared AmountField hero input and rails/RailChip identity across both sheets (single source of truth for colour/glyph/label).
• Send: rail-aware accents, paste + scan, fee-aware spendable max (offboard fee comes from change, so Max now reserves it).
• Receive: tabbed Ark / On-chain / Lightning with per-rail QR + caption.

Deps / config

• Bump ark-* SDK to v0.9.3 (sends x-build-version satisfying the ASP gate).
• Add tauri-plugin-clipboard-manager (+ capability) for paste; dotenvy.