Reject non-integer bounty fields

[nicolatrozzi]

Refs #228

Summary

• Add shared ledger-service integer guards for bounty mutation fields.
• Reject boolean and non-integer issue_number/max_awards values when creating bounties.
• Reject boolean and non-integer bounty_id values before direct pay_bounty() or close_bounty() calls can treat True as bounty id 1.

Repro Before Fix

Direct ledger-service calls could pass values such as issue_number=True, max_awards=True, or bounty_id=True. Because Python booleans are integers (True == 1), those values could create or mutate bounty #1-style records instead of being rejected as malformed input.

Verification

• ./.venv/bin/python -m pytest tests/test_ledger.py::test_create_bounty_rejects_non_integer_issue_number_and_max_awards tests/test_ledger.py::test_bounty_mutations_reject_boolean_bounty_ids -q -> 2 passed
• ./.venv/bin/python -m pytest -q -> 207 passed, 2 warnings
• ./.venv/bin/python -m ruff format --check . -> 37 files already formatted
• ./.venv/bin/python -m ruff check . -> all checks passed
• ./.venv/bin/python -m mypy app -> success
• ./.venv/bin/python scripts/docs_smoke.py -> docs smoke ok
• ./.venv/bin/python scripts/check_agents.py -> AGENTS.md ok
• git diff --check -> clean

No secrets, wallet material, private vulnerability details, deployment values, payout details, or MRWK price claims are included.

[MolhamHamwi]

No blockers found.

Evidence checked:

• Inspected app/ledger/service.py and confirmed the new _required_int / _required_positive_int helpers reject Python bool values before True == 1 can create or mutate bounty records, while preserving the existing positive-range checks and the max_awards > 1_000 cap.
• Inspected tests/test_ledger.py and confirmed coverage rejects boolean/float issue_number and max_awards, plus boolean bounty_id for both pay_bounty() and close_bounty().
• Verified this is scoped to ledger validation and does not touch payout proof metadata, wallet material, deployment configuration, or public pricing text.
• Ran local validation on PR head 2d0e742: focused new tests -> 2 passed; broader ledger/webhook suite -> 31 passed; Ruff check passed; Ruff format check already formatted; git diff --check origin/main...HEAD -> clean.
• Checked GitHub shows the PR merge state clean and the hosted Quality, readiness, docs, and image checks check successful.

[nicolatrozzi]

Closing this one because PR #245 was submitted just before it and covers the same bounty integer-field guard. I opened the distinct non-string service-input fix separately as #251.