fix: validate claim amount against coverage limit

[edehvictor]

Closes #698

Summary

This change adds a coverage-limit validation step to manual claim submission. Before a claim record is created or a Soroban transaction is submitted, the service now loads the policy product and compares the policy claim amount with the configured maximum coverage.

What Changed

• Added a guard in ClaimsService.submitClaim for policies whose stored coverage exceeds the product coverage limit.
• Added a clear 400 Bad Request response describing the requested claim amount and the maximum permitted amount.
• Added a not-found response when the policy references a product that no longer exists.
• Kept duplicate-claim checks and on-chain submission after validation so invalid claims cannot create records or trigger payouts.

Testing

• Not run, per request.
• No install, build, test, or CI check was performed.

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