feat(03-01): add 8 Tier 4 Chinese providers (DeepSeek, Zhipu, Moonshot, Qwen, Baidu, ByteDance, 01.AI, MiniMax)

- DeepSeek, Moonshot, Qwen use documented sk- prefix patterns
- Zhipu, Baidu, ByteDance use keyword-only detection (no documented key format)
- All dual-located in providers/ and pkg/providers/definitions/

providers/baidu.yaml

@@ -0,0 +1,19 @@
+format_version: 1
+name: baidu
+display_name: Baidu ERNIE (Wenxin)
+tier: 4
+last_verified: "2026-04-05"
+keywords:
+  - "wenxin"
+  - "ernie"
+  - "BAIDU_API_KEY"
+  - "QIANFAN_AK"
+  - "QIANFAN_SK"
+  - "aip.baidubce.com"
+  - "qianfan"
+verify:
+  method: POST
+  url: ""
+  headers: {}
+  valid_status: []
+  invalid_status: []