AI网关新增xAI格式TTS端点与过滤弃用模型开关

- POST /ai/v1/tts:xAI 官方 TTS 格式转换层(text/voice_id→input/voice),复用 Speech 编排,model 缺省 xai.grok-tts;实测 output_format/speed 透传生效
- 「过滤弃用模型」开关(GET/PUT /api/v1/ai-settings,settings 表持久化):开启后已宣布弃用(未退役)模型从列表与路由排除;同步入库与退役提醒不受影响
- AI 网关文档更名 docs/AI网关.md,补 tts 矩阵段与开关说明;README 引用同步
- CHANGELOG 0.5.0(0.4.0 已发版冻结);DASH_VERSION v0.5.0

internal/api/aigateway_test.go

@@ -103,6 +103,10 @@ func TestAiGatewayKeyModelRestrict(t *testing.T) {
 			`{"model":"ghost-model","query":"q"}`, 400, []string{"invalid_request_error"}},
 		{"moderations 空 input 拒绝", "open-key-12345", "/ai/v1/moderations",
 			`{"input":[]}`, 400, []string{"invalid_request_error"}},
+		{"tts 缺 language 拒绝", "open-key-12345", "/ai/v1/tts",
+			`{"text":"你好"}`, 400, []string{"invalid_request_error"}},
+		{"tts 白名单外拦截", "limited-key-1234", "/ai/v1/tts",
+			`{"model":"meta.llama-3.3-70b-instruct","text":"你好","language":"zh"}`, 404, deny},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {