docs(api): expand backend route and auth interface docs

[cursor]

Update API documentation with a verified route/middleware matrix, SuperTokens runtime auth endpoints, sync operational header requirements, and runbook-ready examples for maintain-all and debug/sync interfaces.

  

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Note

Low Risk
Documentation-only changes; no runtime behavior, security, or data-handling logic is modified.

Overview
Updates docs/api-documentation.md with a more explicit route-by-route and middleware breakdown across calendars, users, priorities, sync, and events (including resolved env-based paths and write/Google-connection requirements).

Clarifies authentication by documenting the dev-only /api/auth/session contract and listing SuperTokens-managed runtime endpoints under /api.

Adds a new Operational Headers section documenting x-comp-token and Google x-goog-* requirements and includes a curl example for /api/sync/maintain-all.

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