fix(explorer): re-read allowances at the approval block

Parent tracker: #436
Owning PR: #426
Depends on: #441 / PR #425

## Goal

Use the allowance at the approval receipt block before deciding whether approval succeeded or needs recovery.

## Scope

- Wait for the approval receipt.
- Re-read allowance at that receipt's block.
- Use that value for mismatch and retry decisions.

## Non-goals

- Changing approval policy or token selection.
- Adding an unbounded retry loop.
- Restacking, merging, or otherwise changing PR state.

## Acceptance criteria

- A successful approval is not rejected because an earlier block is read.
- A genuine post-receipt allowance mismatch still fails safely.
- The additional RPC read is bounded to the approval flow.
- Focused tests cover the receipt-block read and mismatch handling.

## Performance

Performance is relevant only to the bounded extra RPC read; the change must not add polling or an unbounded retry.

## Delivery

PR #426 remains based on PR #425 while the stack is open. After its predecessor merges, retarget it to staging and revalidate the exact head.

Start with the approval flow and its receipt handling, then trace how allowance is read and how mismatch and retry decisions are made. Add focused tests for the receipt-block read and mismatch handling, confirming the extra RPC read is bounded and no polling is introduced. PR #426 is the owning work and depends on PR #425.

Written by the indexing model from the issue text.