fix: resolve issues #899 #900 #901 #902

[cephas360]

#899 — Settlement fee calculation overflow for large amounts

• contracts/settlement/src/lib.rs: replaced bare += with checked_add for total_weight (initialize) and approval_weight (approve_settlement) to return InvalidWeightSum instead of silently wrapping on u64 overflow.
• COMEBACKHERE-contracts/contracts/treasury/src/lib.rs: same checked_add guards applied to initialize and approve_settlement for consistency across both contract trees.

#900 — Contract event indexer skips events at a ledger boundary

• comebackhere-backend/src/indexer.ts: pollOnce previously set both startLedger and cursor to undefined on a fresh start (cursor === '0'), which left the RPC with no starting point and caused the first ledger's events to be skipped. Fixed by passing startLedger: 1 for the initial poll and switching to cursor-based pagination only once a real paging token has been persisted.

#901 — Compliance lookup failure treated as an approval

• comebackhere-frontend/src/utils/compliance.ts: getAddressStatus now wraps both the network call and simulation check in explicit try/catch blocks and re-throws with unambiguous error messages that make it clear the status is unknown. Added checkAddressAllowed(), a fail-closed wrapper that returns { status: 'Blocked' } on any error so a network hiccup can never silently grant access.

#902 — Settlement webhook uses outdated invoice status

• comebackhere-backend/src/services/treasury-indexer.ts: the settlement_executed webhook previously fired with only the raw on-chain event data before the DB write had been committed. Fixed by reading the updated settlement record from MongoDB (via findOne) immediately after processSettlementExecuted() and including the authoritative status, merchant_address, amount, and token fields in the webhook payload.

chore: update .gitignore

• Added test snapshot patterns (.snap.bak, allure-results/allure-report/, jest-html-reporters-attach/), additional lock-file variants, OS metadata (ehthumbs.db, Desktop.ini, $RECYCLE.BIN/), temp/scratch files (.tmp, *.temp, *.bak, *.orig, .rej), debug artifacts (.cpuprofile, *.heapprofile, *.heapsnapshot), and Soroban local-dev artifacts (.soroban/, **/identity/, wasm-pack.log).

Pull Request

Summary

• Describe the purpose of this PR in one or two sentences.

Checklist

• PR description includes: Closes #[issue_id]
• Tests added or updated
• ABI snapshot updated if contract sources changed (abis/ and COMEBACKHERE-contracts/)
• Screenshots attached if UI changed
• Documentation updated if needed

Notes

• For contract changes, verify ABI snapshot hygiene with make check-abi-snapshots.
• For UI changes, include screenshots or screen recordings to help reviewers.
  closes SAMPLE 053: Settlement fee calculation overflows for a large amount #899
  closes SAMPLE 054: Contract event indexer skips events at a ledger boundary #900
  closes SAMPLE 055: Compliance lookup failure is treated as an approval #901
  closes SAMPLE 056: Settlement webhook uses an outdated invoice status #902

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