feat: add agent trust contract proof page

[stevenchouai]

Summary

• Adds examples/reports/trust-contract.html, a static public page that maps trace evidence to score, permission tier, and stop condition.
• Links the page from the root README and report README.
• Adds deterministic tests that check the page is linked, self-contained, and free of obvious private-path/token/network surfaces.

Test plan

• python -m pytest
• python -m compileall src
• git diff --cached --check

Privacy

• No private vault excerpts, employer details, Feishu IDs, account IDs, local paths, external assets, or third-party named learning cards.