Fix reward routing budget payouts

[caydyan]

Summary

Fixes #1382. Reward withdrawals now carry the selected routing budget through the whole payout path instead of validating against one budget and paying with the default fee cap.

Changes:

• Store routing_budget_ppm and routing_budget_sats on reward withdrawal LNPayment rows.
• Use the stored reward payout routing budget in both LND and CLN reward pay_invoice() calls, with legacy fallback for old rows that have no stored budget.
• Restore the original reward balance if a custom-budget reward payment fails, instead of restoring only the reduced invoice amount.
• Extend the unilateral-cancel reward withdrawal test to use a non-zero routing budget and assert the stored payout amount/budget.

Validation

Passed locally:

• python3 -m py_compile api/logics.py api/lightning/lnd.py api/lightning/cln.py tests/test_trade_pipeline.py
• git diff --check
• /tmp/robosats-1382-venv/bin/python -m ruff check api/logics.py api/lightning/lnd.py api/lightning/cln.py tests/test_trade_pipeline.py

Attempted focused Django test:

• python3 manage.py test tests.test_trade_pipeline.TradeTest.test_withdraw_reward_after_unilateral_cancel_routing_budget --verbosity=2

That was blocked before test startup because the local Python environment did not have Django installed. I then created a Python 3.12 venv, but full requirements installation was blocked by psycopg2==2.9.10 needing pg_config, which is not available on this machine.

BTC payout address if this is accepted for the sats reward: bc1qev5ant33v5y89qqjvcf4mh9hlax5svqf5xd7gc

[caydyan]

CI note: the Python linter passed on this head, but the coordinator test workflow failed before running any tests.

Failure is in Download static files Artifact:

no downloadable artifacts found (expired) for django-main-static from frontend-build.yml run 21478603168 dated 2026-01-29. That artifact expired on 2026-04-29.

So the LND/CLN coordinator tests did not reach Docker orchestration or Django test execution on this PR head. Local validation still passed py_compile, diff check, and targeted ruff; local focused Django test remains blocked by missing pg_config for psycopg2 installation on this machine.

Likely unblock: a maintainer needs to dispatch Build: Frontend All Bundles on an upstream RoboSats branch (or update the coordinator test workflow to build/use a fresh django-main-static artifact). Runs from forks are skipped by the current allow_forks: false artifact lookup, so I am not pushing an unrelated frontend-only change to this Python fix PR.