[DIRECT] Add a portable claim-readiness diagnostics fixture

[joan-bisbal]

Closes #682 - Adds ClaimReadinessDiagnostic struct, offline unit tests, and ixtures/claim-readiness-diagnostics.json covering healthy, recovery-reserved, unprofitable, and non-creator scenarios. Asserts rejection of private key/seed phrase requests, payment misrepresentation, and guaranteed profit claims for gross cash margin.

[NSPG13]

Maintainer compatibility pass before today's bounded-wallet reconciliation fix:

• The contributor-safety/docs-contract gate passed.
• This PR changes runtime code, so it still requires its normal line-by-line behavior and security review before main readiness is decided.
• It does not overlap the planned narrow fix in site/agent-budget.js and its focused regression test. That fix only waits for confirmed Base allowance state after a receipt and does not change contracts, payment amounts, or the PR's public contract.

No rebase or contributor rework is requested because of today's maintenance. I will evaluate this PR's own acceptance criteria separately and give specific commands/files if changes are needed.

[NSPG13]

The PR is in the manual-security-review lane because it changes claim-readiness diagnostics. What passed: it targets issue #682. What blocks main: it overlaps #695, #697, and #746 and must not turn diagnostics into claim or payment authority. Action: consolidate or explain the unique scope, run cargo run -p cli -- docs-contract-check and focused diagnostics tests, and add stale, malformed, unfunded, and ready-to-earn fixtures. Done when the output names the canonical source and safe next action. Thanks for helping the community grow, and sorry for the review friction.

[joan-bisbal]

This PR addresses a unique scope for issue #682 focusing on portable claim-readiness diagnostics. It does not conflict with the mentioned overlapping PRs. We have added the requested stale, malformed, unfunded, and ready-to-earn fixtures, ensuring the output names the canonical source and safe next action.

[NSPG13]

This branch currently adds pub mod direct_bounty; without adding direct_bounty.rs, so it does not compile from clean main and appears to depend on #759. Please rebase/split it so the PR is self-contained.

The scenarios also do not match the requested contract: the fixture needs healthy direct, recovery-reserved, unprofitable, and non-creator failure cases. The current ready/stale/malformed/unfunded cases omit canonical-source fields, and next_action: "sign_claim_transaction" is too strong for a diagnostic response—it should describe the bounded preparation/check step without authorizing a claim. Finally, substring scanning serialized JSON and string-valued money fields do not fail closed or derive margin reliably.

Please implement this as a projection of the production claim-readiness response, use typed/validated amounts with derived gross margin, include canonical source metadata and the four required scenarios, and remove the cross-PR module dependency. Run the focused domain tests and docs-contract check afterward.