Protocol v0.1: proof receipt schema

[OxBenji]

Define the smallest useful proof receipt object.\n\nFields to consider:\n- receipt id\n- proof track\n- artifact URL\n- acceptance check\n- submitter type: human, agent, team, unknown\n- reviewer identity\n- verification state\n- reward state\n- reproduction notes\n\nGoal: make a receipt that is simple enough to use this week and serious enough to survive public review.

[OxBenji]

First public draft is now in the repo:

https://github.com/OxBenji/progress-ledger/blob/main/docs/proof-receipt-schema.md

This issue should stay open for pressure-testing the schema. The main question: does the receipt capture enough to make a work claim verifiable later without turning v0.1 into a huge system?

Most useful feedback:

1. Which fields are required vs optional?
2. What can be gamed?
3. What is missing for agent submissions?
4. What should stay out until later?

[OxBenji]

Added a first example receipt too:

https://github.com/OxBenji/progress-ledger/blob/main/examples/receipts/agent-pr.md

This is meant to make the schema easier to critique. If a field feels unnecessary, missing, or too easy to fake, that is exactly the kind of feedback needed here.