docs(rfp): add RFP evidence map positioning contracts as supporting w…

[Muhamadmust]

Closes #167

Description

Resolves #167 by creating docs/RFP-EVIDENCE-MAP.md, providing an evidence map that positions accensa-contracts as shipped prior work supporting our SCF RFP submission.

Key Content Included

• Stale Document Flag: Flagged RFP-ALIGNMENT.md as outdated following the creation of x402-facilitator-stellar.
• Shipped Work Inventory: Documented ReceiptAnchor, RefundVault, soroban-sdk 27.0.4 deployment, test coverage, storage/TTL strategies, ADRs, and CI policies with relative links.
• RFP §4 Mapping: Mapped repository capabilities directly to §4 evaluation criteria (Soroban experience, payment infrastructure, security discipline).
• Boundary Clarification: Explicitly separated receipt verification from x402 verify/settle deliverables.
• Genuine Connections: Highlighted shared architectural concepts (ADR-002 upto scheme, registry patterns, decimal semantics).
• Maturity Disclosures: Stated testnet-only status, pre-1.0 release, and lack of a formal third-party audit.

Verification Checklist

• cargo fmt --all -- --check passes cleanly.
• cargo clippy --workspace --all-targets -- -D warnings passes with zero warnings.
• cargo test passes.
• cargo build --target wasm32v1-none --release succeeds.

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[mergekeeper]

MergeKeeper review

Scope: in scope for linked issue #167.
Verdict: clean

The pull request successfully implements the RFP evidence map under docs/RFP-EVIDENCE-MAP.md, addressing all requirements of issue #167.

Reviewed commit: 96ed91c6271fd1ca2c040afe93bdb6abaff0b623.
CI and merge eligibility are checked separately.

[mergekeeper]

MergeKeeper merge status

Status: blocked
PR state: open
Mergeability: mergeable
Checked commit: 96ed91c6271fd1ca2c040afe93bdb6abaff0b623.

Reason: One or more required CI checks failed.

Failing checks:

• test - view details
• build-wasm - view details
• clippy - view details
• fmt - view details

Next steps:

1. Open the failing check details above and fix the reported error.
2. Run the same checks locally where possible.
3. Commit and push the fix.
4. MergeKeeper will automatically re-review the updated PR.