feat: add dynamic x-api-provider and reasoning_effort support

- Add per-model provider configuration in config.json
- Implement getModelProvider() to fetch provider from model config
- Update all header generators to accept dynamic provider parameter
- Add reasoning_effort field handling for common endpoint type
- Support auto/low/medium/high/off reasoning levels for common models

This enables flexible multi-provider support and reasoning control
across different endpoint types (anthropic, openai, common).

config.json

@@ -25,48 +25,64 @@
       "name": "Opus 4.1",
       "id": "claude-opus-4-1-20250805",
       "type": "anthropic",
-      "reasoning": "auto"
+      "reasoning": "auto",
+      "provider": "anthropic"
     },
     {
       "name": "Haiku 4.5",
       "id": "claude-haiku-4-5-20251001",
       "type": "anthropic",
-      "reasoning": "auto"
+      "reasoning": "auto",
+      "provider": "anthropic"
     },
     {
       "name": "Sonnet 4.5",
       "id": "claude-sonnet-4-5-20250929",
       "type": "anthropic",
-      "reasoning": "auto"
+      "reasoning": "auto",
+      "provider": "anthropic"
     },
     {
       "name": "GPT-5",
       "id": "gpt-5-2025-08-07",
       "type": "openai",
-      "reasoning": "auto"
+      "reasoning": "auto",
+      "provider": "openai"
     },
     {
       "name": "GPT-5-Codex",
       "id": "gpt-5-codex",
       "type": "openai",
-      "reasoning": "off"
+      "reasoning": "off",
+      "provider": "openai"
     },
     {
       "name": "GPT-5.1",
       "id": "gpt-5.1",
       "type": "openai",
-      "reasoning": "auto"
+      "reasoning": "auto",
+      "provider": "openai"
     },
     {
       "name": "GPT-5.1-Codex",
       "id": "gpt-5.1-codex",
       "type": "openai",
-      "reasoning": "off"
+      "reasoning": "off",
+      "provider": "openai"
     },
     {
       "name": "GLM-4.6",
       "id": "glm-4.6",
-      "type": "common"
+      "type": "common",
+      "reasoning": "off",
+      "provider": "fireworks"
+    },
+    {
+      "name": "Gemini-3-Pro",
+      "id": "gemini-3-pro-preview",
+      "type": "common",
+      "reasoning": "auto",
+      "provider": "google"
     }
   ],
   "dev_mode": false,