fix(#307): replace hardcoded expiration ledger with live getLatestLed…

[Danielodingz]

Closes #307

fix(#307): ApproveForm — replace hardcoded expiration ledger with live ledger sequence

Problem

Both the simulate (handleCheck) and submit (onSubmit) paths in
ApproveForm.tsx computed the SEP-41 expiration_ledger using a
hardcoded base of 1_000_000:

// Before (broken)
const ledger = 1000000 + parseInt(formData.expirationDays || "365") * 10800;

This caused two compounding bugs:

1. Stale base — Testnet and Mainnet ledger sequences are well above
   1,000,000. The computed ledger was already in the past, so Soroban
   rejected the allowance (or created one that expired immediately).
2. Wrong rate — 10800 ledgers/day assumes ~8 s/ledger
   (86400 / 10800 = 8). Soroban closes ledgers at ~5 s, so the
   allowance window was off by ~60%.

The vesting flow in AdminPanel already handles this correctly
(getLatestLedger().sequence + days * 17280). ApproveForm was the
outlier.

Fix

frontend/components/forms/ApproveForm.tsx

• Import fetchCurrentLedger from @/lib/stellar.
• Add a single shared getExpirationLedger(days) helper that calls
  fetchCurrentLedger(networkConfig) and returns
  currentLedger + parseInt(days) * 17280.
• Both handleCheck (simulate) and onSubmit (submit) now call the
  same helper — they cannot drift.

// After (correct)
const getExpirationLedger = async (days: string): Promise<number> => {
  const currentLedger = await fetchCurrentLedger(networkConfig);
  return currentLedger + parseInt(days || "365") * 17280;
};

frontend/components/AllowanceList.tsx (follow-on)

• Add optional currentLedger?: number prop to AllowanceListProps.
• Add ledgerToExpiryInfo(expirationLedger) helper that converts a
  ledger number to a human-readable expiry date and countdown string
  (e.g. Jun 30, 2026 · 364d 23h remaining / Expired) using
  5 s/ledger arithmetic.
• Rendered below the existing raw ledger number when currentLedger
  is supplied (fully backwards-compatible — callers that don't pass the
  prop see no change).

Testing

• Set "365 days" in the Approve form → preflight check and submit both
  compute `sequence + 6,

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[Danielodingz]

Hello @zachyo please review PR and merge. Thank You

[Danielodingz]

Hello @zachyo please review PR and merge. Thank you