feat: add view_image tool and optimize web fetch tools

Add image viewing capability for vision-enabled models with ViewImageMiddleware and view_image_tool. Limit web_fetch tool output to 4096 characters to prevent excessive content. Update model config to support vision capability flag.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

config.example.yaml

@@ -21,6 +21,7 @@ models:
     api_key: $OPENAI_API_KEY  # Use environment variable
     max_tokens: 4096
     temperature: 0.7
+    supports_vision: true  # Enable vision support for view_image tool
 
   # Example: Anthropic Claude model
   # - name: claude-3-5-sonnet
@@ -29,6 +30,7 @@ models:
   #   model: claude-3-5-sonnet-20241022
   #   api_key: $ANTHROPIC_API_KEY
   #   max_tokens: 8192
+  #   supports_vision: true  # Enable vision support for view_image tool
 
   # Example: DeepSeek model (with thinking support)
   # - name: deepseek-v3
@@ -38,6 +40,7 @@ models:
   #   api_key: $DEEPSEEK_API_KEY
   #   max_tokens: 16384
   #   supports_thinking: true
+  #   supports_vision: false  # DeepSeek V3 does not support vision
   #   when_thinking_enabled:
   #     extra_body:
   #       thinking:
@@ -51,6 +54,7 @@ models:
   #   api_base: https://ark.cn-beijing.volces.com/api/v3
   #   api_key: $VOLCENGINE_API_KEY
   #   supports_thinking: true
+  #   supports_vision: false  # Check your specific model's capabilities
   #   when_thinking_enabled:
   #     extra_body:
   #       thinking:
@@ -65,6 +69,7 @@ models:
   #   api_key: $MOONSHOT_API_KEY
   #   max_tokens: 32768
   #   supports_thinking: true
+  #   supports_vision: false  # Check your specific model's capabilities
   #   when_thinking_enabled:
   #     extra_body:
   #       thinking:
@@ -107,6 +112,11 @@ tools:
     use: src.community.image_search.tools:image_search_tool
     max_results: 5
 
+  # View image tool (display local images to user)
+  - name: view_image
+    group: file:read
+    use: src.tools.builtins:view_image_tool
+
   # File operations tools
   - name: ls
     group: file:read