docs: add traceability table for mapping contract changes to acceptan…

[iamdikko]

Closes #515
…ce criteria

• Create docs/traceability-table.md with 6-column table format, worked example, and usage rules
• Update PR template: replace Acceptance Criteria Coverage section with the richer Traceability Table section referencing the new guide
• Update README: add doc link in Documentation section and traceability requirement in Contributing section

Closes #515

Pull Request

Issue Reference

Closes #

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Summary

Contract Functions Changed

Function	Change type (added / modified / removed)	Notes

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Tests Added or Updated

• Happy-path tests added/updated
• Failure and boundary-condition tests added/updated
• Test naming follows the convention in docs/testing.md
• docs/test-coverage.md updated to reflect new or changed tests

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Security Considerations

Security checklist (contract changes only)

• Balance & accounting invariants preserved — see docs/accounting-invariants.md
• Lock state and timed-operation rules unchanged (or documented if changed)
• Token transfer atomicity maintained — see docs/atomicity.md
• require_auth() called on the correct address in every state-changing function
• Storage layout change checklist followed (if applicable) — see docs/storage-change-checklist.md
• Event backward-compatibility policy followed (if applicable) — see docs/event-compatibility-policy.md
• New error codes use ContractError variants with panic_with_error!, not bare panic!
• No secrets, private keys, or credentials committed or logged

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Commands Run

cargo fmt --check
cargo clippy --tests -- -D warnings
cargo test --workspace

• cargo fmt --check — passed
• cargo clippy --tests -- -D warnings — passed
• cargo test --workspace — passed

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CI Status

• All CI checks pass on this branch

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Acceptance Criteria Coverage

Criterion	Met?	Notes