feat(providers): add kimi-coding-cn provider for mainland China users

Cherry-picked from PR #7637 by hcshen0111.
Adds kimi-coding-cn provider with dedicated KIMI_CN_API_KEY env var
and api.moonshot.cn/v1 endpoint for China-region Moonshot users.

agent/model_metadata.py

@@ -24,7 +24,7 @@ logger = logging.getLogger(__name__)
 # are preserved so the full model name reaches cache lookups and server queries.
 _PROVIDER_PREFIXES: frozenset[str] = frozenset({
     "openrouter", "nous", "openai-codex", "copilot", "copilot-acp",
-    "gemini", "zai", "kimi-coding", "minimax", "minimax-cn", "anthropic", "deepseek",
+    "gemini", "zai", "kimi-coding", "kimi-coding-cn", "minimax", "minimax-cn", "anthropic", "deepseek",
     "opencode-zen", "opencode-go", "ai-gateway", "kilocode", "alibaba",
     "qwen-oauth",
     "xiaomi",
@@ -32,7 +32,7 @@ _PROVIDER_PREFIXES: frozenset[str] = frozenset({
     # Common aliases
     "google", "google-gemini", "google-ai-studio",
     "glm", "z-ai", "z.ai", "zhipu", "github", "github-copilot",
-    "github-models", "kimi", "moonshot", "claude", "deep-seek",
+    "github-models", "kimi", "moonshot", "kimi-cn", "moonshot-cn", "claude", "deep-seek",
     "opencode", "zen", "go", "vercel", "kilo", "dashscope", "aliyun", "qwen",
     "mimo", "xiaomi-mimo",
     "qwen-portal",
@@ -211,6 +211,7 @@ _URL_TO_PROVIDER: Dict[str, str] = {
     "api.anthropic.com": "anthropic",
     "api.z.ai": "zai",
     "api.moonshot.ai": "kimi-coding",
+    "api.moonshot.cn": "kimi-coding-cn",
     "api.kimi.com": "kimi-coding",
     "api.minimax": "minimax",
     "dashscope.aliyuncs.com": "alibaba",