serve now uses oidc.DexAuth (single-user allowlist authz, ADR-011) when TAPIR_OIDC_ISSUER is set, falling back to allow-all StubAuth for local dev. Adds the Dex config fields (TAPIR_OIDC_ISSUER/DEX_CLIENT_ID/SECRET/ OIDC_REDIRECT_URL/SESSION_SECRET/ALLOWED_SUBJECT) + Config.DexConfigured(). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>