feat: 添加 VEO3 场景写作和角色定义 SDK

- 新增 gemini-sdk: 基于 Gemini AI 的通用 SDK
- 新增 veo3-scene-writer: VEO3 场景写作专用工具
  - 支持图片/视频附件分析
  - 多轮会话功能
  - VEO3 专业提示词集成
  - 角色一致性管理
- 新增 Veo3ActorDefine: 角色定义专用工具
- 添加完整的示例和文档
- 支持多种输出格式 (文本/JSON/YAML)

cargos/gemini-sdk/examples/basic_usage.rs

@@ -0,0 +1,119 @@
+//! Basic usage example for the Gemini SDK
+
+use gemini_sdk::{GeminiSDK, MessageRequest, Agent};
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    // Initialize SDK
+    let mut sdk = GeminiSDK::new()?;
+
+    // Example 1: Simple text message
+    println!("=== Example 1: Simple text message ===");
+    let request = MessageRequest::text_only("Hello, how are you?");
+    
+    match sdk.send_message(request).await {
+        Ok(response) => {
+            println!("Response: {}", response.content);
+        }
+        Err(e) => {
+            println!("Error: {}", e);
+        }
+    }
+
+    // Example 2: Using an agent
+    println!("\n=== Example 2: Using an agent ===");
+    let agent = Agent::new(
+        "helpful_assistant",
+        "Helpful Assistant",
+        "You are a helpful assistant that provides clear and concise answers."
+    ).with_temperature(0.7);
+    
+    sdk.add_agent(agent);
+
+    let request = MessageRequest::with_agent(
+        "Explain quantum computing in simple terms",
+        "helpful_assistant"
+    );
+
+    match sdk.send_message(request).await {
+        Ok(response) => {
+            println!("Agent response: {}", response.content);
+        }
+        Err(e) => {
+            println!("Error: {}", e);
+        }
+    }
+
+    // Example 3: Message with image attachment (commented out as it requires a real image file)
+    /*
+    println!("\n=== Example 3: Message with image attachment ===");
+    let request = MessageRequest::with_attachments(
+        "What do you see in this image?",
+        vec![Attachment::new("./example.jpg")]
+    );
+
+    match sdk.send_message(request).await {
+        Ok(response) => {
+            println!("Image analysis: {}", response.content);
+        }
+        Err(e) => {
+            println!("Error: {}", e);
+        }
+    }
+    */
+
+    // Example 4: Creating a specialized agent
+    println!("\n=== Example 4: Creating a specialized agent ===");
+    let code_agent = Agent::new(
+        "code_reviewer",
+        "Code Reviewer",
+        r#"You are an expert code reviewer. When given code, you should:
+1. Analyze the code for potential bugs or issues
+2. Suggest improvements for readability and performance
+3. Check for best practices and coding standards
+4. Provide constructive feedback
+
+Always be specific and provide examples when possible."#
+    ).with_temperature(0.3)  // Lower temperature for more focused responses
+     .with_max_tokens(4096);
+
+    sdk.add_agent(code_agent);
+
+    let code_example = r#"
+def fibonacci(n):
+    if n <= 1:
+        return n
+    else:
+        return fibonacci(n-1) + fibonacci(n-2)
+
+print(fibonacci(10))
+"#;
+
+    let request = MessageRequest::with_agent(
+        format!("Please review this Python code:\n\n```python{}\n```", code_example),
+        "code_reviewer"
+    );
+
+    match sdk.send_message(request).await {
+        Ok(response) => {
+            println!("Code review: {}", response.content);
+        }
+        Err(e) => {
+            println!("Error: {}", e);
+        }
+    }
+
+    // Example 5: List all agents
+    println!("\n=== Example 5: List all agents ===");
+    let agents = sdk.list_agents();
+    for agent in agents {
+        println!("Agent: {} (ID: {})", agent.name, agent.id);
+        println!("  Temperature: {}", agent.temperature);
+        println!("  Max tokens: {}", agent.max_tokens);
+        println!("  System prompt: {}...", 
+                 agent.system_prompt.chars().take(50).collect::<String>());
+        println!();
+    }
+
+    Ok(())
+}