refactor: simplify router to OpenAI and OpenRouter providers only

- Remove Gemini direct and DeepSeek provider configurations
- Keep OpenAI (gpt-5.2, gpt-5-mini) and OpenRouter (Gemini 3 models)
- Update documentation and environment examples
- Remove cost column from README providers table

configs/router-config.json

@@ -15,32 +15,13 @@
         "use": [["maxcompletiontokens", { "max_completion_tokens": 16384 }]]
       }
     },
-    {
-      "name": "gemini",
-      "api_base_url": "https://generativelanguage.googleapis.com/v1beta/models/",
-      "api_key": "$GEMINI_API_KEY",
-      "models": ["gemini-2.5-pro"],
-      "transformer": {
-        "use": ["gemini"]
-      }
-    },
-    {
-      "name": "deepseek",
-      "api_base_url": "$DEEPSEEK_API_BASE",
-      "api_key": "$DEEPSEEK_API_KEY",
-      "models": ["deepseek-ai/DeepSeek-V3", "deepseek-chat"],
-      "transformer": {
-        "use": ["deepseek", "enhancetool"]
-      }
-    },
     {
       "name": "openrouter",
       "api_base_url": "https://openrouter.ai/api/v1/chat/completions",
       "api_key": "$OPENROUTER_API_KEY",
       "models": [
-        "anthropic/claude-sonnet-4",
         "google/gemini-3-pro-preview",
-        "openai/gpt-5.2"
+        "google/gemini-3-flash-preview"
       ],
       "transformer": {
         "use": ["openrouter"]