[Feature] Add configurable timeout for tool execution

[QuietyAwe]

Problem

Currently, tool execution timeout is hardcoded to 60 seconds in the shell tool implementation. This affects:

1. exec tool - Shell commands may hang indefinitely if the default timeout is insufficient
2. web_fetch - HTTP requests could timeout at inappropriate times
3. subagent/spawn - Long-running tasks have no configurable timeout

From code inspection:

• pkg/tools/shell.go has a hardcoded timeout: 60 * time.Second
• pkg/config/config.go ExecConfig struct only has EnableDenyPatterns and CustomDenyPatterns
• No way to configure timeout via config file or environment variable

Proposed Solution

Add timeout configuration to ExecConfig:

{
  "tools": {
    "exec": {
      "enable_deny_patterns": true,
      "custom_deny_patterns": [],
      "timeout_seconds": 120
    }
  }
}

Changes needed:

1. Config struct - Add TimeoutSeconds field to ExecConfig
2. Environment variable - Support PICOCLAW_TOOLS_EXEC_TIMEOUT_SECONDS
3. Apply timeout - Use configured timeout in NewExecToolWithConfig
4. Default value - Keep 60 seconds as default for backward compatibility

Benefits:

• Users can increase timeout for long-running operations (e.g., video processing, large file downloads)
• Users can decrease timeout for faster failure detection
• Consistent with other configurable parameters

Related

• Issue [BUG] looping in something #819 mentions "looping in something" which could be related to timeout behavior