feat(api): add speech profile and language-pair routing

[jinyu918]

Summary

Implements Phase 1 of language-pair-based ASR/TTS provider routing.

• Adds versioned contract types for ASR profiles, TTS profiles, and exact language-pair routes.
• Adds PostgreSQL schema for speech_asr_profiles, speech_tts_profiles, and speech_language_pair_routes.
• Normalizes unordered language pairs so zh-CN <-> en-US and en-US <-> zh-CN resolve to the same route.
• Enforces one active route per language pair through a partial unique index.
• Validates that active routes reference enabled, non-retired, capability-compatible ASR and TTS profiles.
• Preserves active language-catalog configuration creation during Phase 1. Strict validation against a complete active speech route is opt-in through NewServiceWithSpeechRouteValidator and will be enabled in production after constructable provider profiles and routes are provisioned.
• Seeds the existing legacy-default profile pair and the en-US / zh-CN route for compatibility.
• Documents profile immutability and the retirement-based replacement flow. No client-writable profile or route CRUD API is introduced.

Validation

• Added contract, route-domain, migration-schema, and PostgreSQL store tests.
• Verified both directions of zh-CN <-> en-US resolve to the same active route.
• Verified duplicate active routes are rejected.
• Verified disabled, retired, or capability-incompatible profiles cannot be used by an active route.
• Verified language configurations without a complete active route are rejected.

Scope

This PR establishes the API data model and validation boundary only. It does not build the realtime provider registry, prepare session bindings, consume language configuration events, or change media/provider protocol handling.

Related issue

• Proposal: 支持按语言对路由多 ASR / 多 TTS Provider #231

[github-actions]

Go coverage

Scope	Current	Baseline	Delta
packages/contracts	87.2%	87.2%	+0.0%
services/api	61.1%	60.8%	+0.3%
services/realtime-audio	78.6%	78.6%	+0.0%
Total	69.3%	69.2%	+0.1%

Base branch: dev · Commit: f6525f5 · Test workflow run

[fennoai]

Found one production regression in the new strict speech-route wiring. Targeted tests pass: go test ./packages/contracts/languages/v1 ./services/api/languages.

[fennoai]

评审结论

整体结构清晰：契约、领域校验、PostgreSQL 存储和迁移职责分离合理；语言对查询使用规范化键和部分唯一索引，查询形态没有明显性能问题；错误包装与单元测试覆盖也较完整。

发现 1 个需要修正的能力完整性问题，已添加行内意见。

[Jerry-Yu-TeslaCoil]

先前两条评审意见（生产默认严格校验会打掉非 en-US/zh-CN 目录对；ResolveSpeechRoute 未要求 TTS 双侧覆盖）在最新提交里都已处理：生产仍走 NewService（严格校验 opt-in），Resolve 路径已要求双侧 TTS。CI 全绿。