Contact messages API

POST /api/messages creates a contact message in the env-selected MessageStore (SQLite / Postgres / DynamoDB).

List and delete messages are available only on the Docker-only admin service (GET|DELETE /api/admin/messages on @tgmc/admin). See admin.md.

Public create validation:

• Non-empty name, email, and body
• Email shape check; max lengths name 100 / email 254 / body 5000
• Best-effort in-memory rate limit (5 creates per client IP per hour), in addition to API Gateway throttling

The public About contact CTA remains mailto: — this API is optional infrastructure, not the primary contact path.