docs(openapi): add automated OpenAPI v3 spec generation & validation guide (#109)

[showmemercy19-rgb]

Adds OpenAPI v3 specification generation documentation.

[github-actions]

All applicable PR CI workflows passed for 9c090d1.

• ci
• security

Ready for maintainer code review.

[armstrongsam25]

Thanks for contributing. I reviewed the full diff against current main and the LETS constitution.

"Swagger UI rendering" contradicts the shipped server: src/lets/api.py:create_app sets docs_url=None and redoc_url=None, exposing normative /v1/openapi.json; constitution XII explicitly requires normative OpenAPI rather than interactive /docs. Please remove that claim and provide actual schema-generation commands, committed protocol/openapi.yaml parity/version checks and the supported consumption path. Two bullets are not the requested generation guide.

Please expand this into complete, source-backed documentation before merge (constitution XI and XII). This head contains no measurable executable lines, so changed-line coverage is not applicable; that should be recorded explicitly in the PR. No tests or candidate code were executed during this review.

[armstrongsam25]

Closing after source-based triage of head 9c090d1. The generation guide consists of two bullets, including Swagger UI rendering, while the shipped server deliberately disables docs/redoc and exposes normative /v1/openapi.json. It includes no generation command or parity/version validation procedure. It supplies an unsupported consumption path rather than the promised guide.

Evidence: normative server OpenAPI surface; actual generator; entire submitted guide.

Triage criterion: unsupported-completion. Closing this unmerged PR does not close an unfulfilled task, delete the contributor branch, or award bounty points. A distinct substantive revision may be reviewed after reopening.