Land reimbursement rounding, campaign gas cushion, and branch cleanup

[AdamSpitz]

Summary

• Replay the assurance-contract claim-share accumulator in foldReimbursements, so forgo and withdrawable amounts match on-chain views when a donation does not divide evenly.
• Cut the fake-data campaign wallet native buffer from 0.05 ETH to 0.001 ETH. It is gas slack, and 0.05 ETH per wallet made a 10-user canary look like it needed about 1 ETH.
• Tell agents to switch back to dev and delete the local feature branch after a PR lands.

[AdamSpitz]

Review receipt.

Reviewed the three commits against origin/dev. foldReimbursements now mints ceiling claim-shares and accrues donations on the 1e36 accumulator, matching AssuranceContracts withdrawable and future-claim views; the two new remainder tests cover an indivisible 1-wei donation and a ceiling mint. The campaign buffer change is a constant plus the matching assertions. The branching.md edit only tells agents to return to dev and delete the merged local branch. No findings.

Reviewed-with: grok
Reviewed-files: 5
Reviewed-commit: f811351