Validate LoanManager min score bounds

[Lucas-FManager]

Summary

Refs #941.

This hardens LoanManager::set_min_score so the admin setter follows the same Result<(), LoanError> pattern as the other guarded configuration setters and rejects unsafe score bounds.

Approach

• Added a local MAX_CREDIT_SCORE ceiling of 850, matching the RemittanceNFT score cap referenced by the issue.
• Changed set_min_score to return Result<(), LoanError>.
• Rejects 0 and values above 850 with LoanError::InvalidConfiguration before writing storage.
• Keeps the existing successful update path, including min_score_updated, unchanged after validation succeeds.
• Added focused tests for a normal update, boundary value 850, and rejected out-of-bounds values.

Security

• Prevents a misconfigured or compromised admin flow from setting min_score > 850, which would make all borrowers fail the score gate.
• Prevents min_score = 0, which would effectively disable the score gate.
• Does not alter loan balances, repayments, pool transfers, collateral logic, or borrower state.
• Failed updates do not write the new config value.

Verification

• docker run --rm -v "C:\\Users\\ADMIN\\.openclaw\\github-jobs\\remitlend:/work" -w /work/contracts rust:1.95 bash -lc "/usr/local/cargo/bin/cargo test -p loan_manager set_min_score"
• git diff --check

[Lucas-FManager]

CI note after re-checking the failing workflow:

• CodeQL and supply-chain checks are passing.
• The contracts failure is from contracts/lending_pool/src/test.rs, which is outside this PR's loan_manager scope.
• The backend and frontend failures are also full-repo lint/format issues outside this PR.
• The targeted verification for this branch still holds: cargo test -p loan_manager set_min_score passed, and cargo fmt -p loan_manager -- --check passed in Docker.

I am leaving the branch scoped to the min-score validation fix unless you want a separate cleanup for the repository-wide formatting issues.