fix(graphql-server): parse interval auth cookie durations

[Zetazzz]

Summary

• Add a shared PgInterval type for auth settings loaded from PostgreSQL interval columns.
• Add interval conversion helpers for seconds and milliseconds.
• Parse interval objects in session cookie duration handling while preserving existing numeric string behavior.

Why

app_settings_auth.cookie_max_age and remember_me_duration are PostgreSQL interval columns. The pg driver returns them as interval objects, but the cookie helper only parsed string seconds, causing configured session durations to fall back to the default.

Validation

• pnpm --filter @constructive-io/graphql-server test -- cookie.test.ts pg-interval.test.ts
• pnpm --filter @constructive-io/express-context build
• pnpm --filter @constructive-io/graphql-server build
• git diff --check