fix(atomic_swap): pay insurance claims from per-policy reservations

[DevMusa001]

PR Summary

Pay insurance claims from per-policy reservations

Problem

claim_insurance computed actual_payout = if pool >= payout { payout } else { pool }, paying every policy from one fungible InsurancePool(token) balance. Two valid policies on the same token could be claimed in sequence, and the second claimant silently got a partial payout or zero, with no error separating "your claim is invalid" from "someone drained the pool first".

Fix

• New keys InsuranceReserved(swap_id) and InsuranceReservedTotal(token), kept as DataKey variants rather than SwapRecord fields so existing test literals compile untouched.
• A reservation equal to the coverage amount is carved wherever the premium is collected: accept_swap and batch_accept_swaps.
• claim_insurance pays that policy's own reservation or panics. It never transfers a reduced amount.
• Release is centralized in save_swap instead of duplicated across ~20 status transitions, and is skipped while a swap is still flagged InsuranceClaimable.

New errors

Error	Code	Meaning
InsuranceNotReserved	66	Policy holds no reservation
InsufficientInsuranceReserve	67	Claim valid, pool under-collateralized, nothing transferred

New API

• get_insurance_pool_status(token) returns InsurancePoolStatus { token, balance, reserved, collateralized, shortfall }, so under-collateralization is observable before it causes a failed payout.
• get_insurance_reservation(swap_id).
• fund_insurance_pool(funder, token, amount). Not in the original scope but load-bearing: a policy contributes 2% of price and reserves 100% of it, so a premium-only pool is under-collateralized by construction and every claim would panic #67.

Tests

Five tests in insurance_reserve_tests, all issuing policies through the real initiate_swap then accept_swap path:

• Two policies both paid in full, A then B and B then A.
• Claim against an under-collateralized pool panics #67.
• Claim with no reservation panics #66.
• Shortfall visible via get_insurance_pool_status before any claim.

cargo build --workspace and cargo test --workspace are green, including the Redis-gated api-server tests.

Unchanged

Premium calculation, risk-factor, and tiering logic are untouched. The premium stays 2% of price in both initiate_swap and batch_initiate_with_insurance.

Known issue not fixed here

reveal_key sets InsuranceClaimable(swap_id) and then calls panic_with_error(InvalidKey), which reverts the write, so the flag cannot persist and claim_insurance is unreachable through that path. Pre-existing, and fixing it changes reveal_key's revert semantics. Tests seed the flag directly.

Closes

Closes #789