feat: add fee selection ui

[nicoletting]

What changed

Adds the Fee Selection UI for the send Confirm screen (body-only, pure components):

• AmountFeeGroup — the Amount + Est. Fee group. Two independent tap zones on the Est. Fee row:
  • fee amount (right) → opens the Fee & Speed sheet — Kaspa-native KAS only (feeSelectable)
  • Est. Fee label (left) → opens the existing Est. Fee breakdown sheet
• FeeSpeedSheet — bottom sheet to pick transaction speed (Low / Medium / High), with a network-status badge (Smooth / Busy / Congested) and a "Recommended" pill.
• StatusPill — added a backward-compatible icon="dot" variant (used by the network-status badge). Existing tx-status callers are unaffected.

Why

Notion: Fee Selection & Custom Transaction Fee UI (Mobile). Lets Kaspa-native KAS transactions pick a custom fee/speed; Layer-2 (Kasplex / Igra) and Kaspa-network KRC20 use the non-selectable default.

For Paul to confirm

1. Per-network default — FeeSpeedSheet currently defaults selected/recommended to medium. Please confirm the default speed for each network state (Smooth / Busy / Congested) and select that option by default.
2. AmountFeeGroup -Default (Non-selectable variant) — feeSelectable={false} is for networks that can't custom-set fee. Use it or leave it — your call.
3. ≈ on USD — design shows ≈ $24,000 (no "USD" suffix). Production formatCurrency outputs $24,000 (no ≈). Is ≈ dropped because the USD shown is exactly the real value? If it's an approximation, please prepend "≈ ".
4. Est. Fee tooltip NOT built — I only wired the left zone to your existing EstFeeSheet component. No new tooltip/breakdown sheet was built.

Design tokens used

white["5%"], border.b200, borderRadius.2xl/3xl/xl/full, spacing.*, typography.t900/t800/t600/t500, background.bg100/bg200/bg400/bg500, success/warning/error.*, info.*, textStyles.*

Testing

• Storybook web preview (npm run preview)
• Android phone via Expo Go
• Component states: AmountFeeGroup (Default / KaspaSelectable / LongAmount), FeeSpeedSheet (Smooth / Busy / Congested)
• UAT: confirm the AmountFeeGroup card bg (white["5%"]) sits consistently next to the other confirm-page cards (kastle-mobile uses bg-background-950/5 — near-identical faint tint, verify on device)

[github-actions]

🎨 Storybook Preview Ready!

Your Storybook preview has been deployed and is available at:

🔗 Preview URL: https://forbole.github.io/kastle-ui/preview/pr-51/

📝 What's included:

• All components from this PR
• Interactive component playground
• Documentation and examples

💡 This preview updates automatically when you push new commits to this PR.

🗑️ Preview will be cleaned up when the PR is merged or closed.;