feat: populate content_length and max_output from official docs (#17836)

## Summary

- Verify and populate `content_length` (context window) and `max_output`
(max generation tokens) for all **478 chat/vision models** across **47
provider configs**
- Data sourced from **official API documentation** via 12 parallel
agents + targeted web verification
- Update Go test assertions to match verified values

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

conf/models/siliconflow.json

@@ -16,7 +16,8 @@
   "models": [
     {
       "name": "Pro/deepseek-ai/DeepSeek-V4-Pro",
-      "max_output": 1048576,
+      "content_length": 1048576,
+      "max_output": 393216,
       "model_types": [
         "chat"
       ],
@@ -30,7 +31,8 @@
     },
     {
       "name": "Pro/deepseek-ai/DeepSeek-V4-Flash",
-      "max_output": 1048576,
+      "content_length": 1048576,
+      "max_output": 393216,
       "model_types": [
         "chat"
       ],
@@ -44,7 +46,8 @@
     },
     {
       "name": "Pro/moonshotai/Kimi-K2.6",
-      "max_output": 262144,
+      "content_length": 262144,
+      "max_output": 65536,
       "model_types": [
         "chat",
         "vision"
@@ -59,7 +62,8 @@
     },
     {
       "name": "Pro/zai-org/GLM-5.1",
-      "max_output": 204800,
+      "content_length": 200000,
+      "max_output": 128000,
       "model_types": [
         "chat"
       ],
@@ -73,6 +77,7 @@
     },
     {
       "name": "qwen/qwen3-8b",
+      "content_length": 131072,
       "max_output": 32768,
       "model_types": [
         "chat"
@@ -83,7 +88,8 @@
     },
     {
       "name": "qwen/qwen3.5-4b",
-      "max_output": 262144,
+      "content_length": 262144,
+      "max_output": 32768,
       "model_types": [
         "chat"
       ],
@@ -93,7 +99,8 @@
     },
     {
       "name": "tencent/hunyuan-mt-7b",
-      "max_output": 32768,
+      "content_length": 32768,
+      "max_output": 8192,
       "model_types": [
         "chat"
       ],