fix(openai): include omitted tier in all fast rules

[xuhaihan]

Summary

• make service_tier=all match requests that omit service_tier
• keep service_tier=missing as the narrower matcher for omitted-tier requests only
• apply the same behavior to HTTP and Responses WebSocket requests
• align admin UI text and Chinese documentation with the actual semantics

Context

Follow-up to #5833. That PR introduced the explicit missing matcher while preserving a legacy interpretation where all covered only explicitly supplied tiers. For an administrator selecting "all tier values", omission is also a tier state; otherwise a user-scoped force_priority rule silently misses normal Codex requests that omit the field.

Validation

• go test ./internal/service -run "Test(ApplyOpenAIFastPolicyToBody|WSResponseCreate)" -count=1
• pnpm exec vitest run src/i18n/__tests__/openaiFastPolicyLocales.spec.ts
• git diff --check
• sensitive-content scan