docs: implement pull request template and acceptance criteria traceab…

[iamdikko]

Closes #395
…ility documentation

Related Issue

• Closes #

Implementation Scope

• Problem addressed:
• Modules changed: (e.g. src/payments/validation.ts, src/errors/index.ts)
• Public API impact: (none / new export / breaking change — explain if breaking)

Tests Added / Changed

• New tests added: (list files, e.g. tests/validation.test.ts)
• Failure paths covered: (negative inputs, error classification, edge cases)
• Docs-only / config-only PR — tests not applicable because:

Commands Run (local verification)

• npm run presubmit passed locally (or npm run verify)
• npm run coverage:baseline reviewed for changed modules (or N/A: docs-only)

<paste `npm run presubmit` / `npm run coverage:baseline` output summary here>

CI Status

• All CI checks are passing (or red-only for a documented, pre-existing reason)
• CI run link (if needed):

Acceptance Criteria Coverage

• Criterion 1:
• Criterion 2:
• Criterion 3:

Contributor Self-Review

• Self-review form completed and attached

Contribution Quality Gate

• I reviewed the Contribution Quality Gate and believe this PR meets it
• Implementation is complete (not a stub / docs-only when behaviour was required)
• Tests, CI, docs, and acceptance criteria sections above are filled

Reviewer Notes