docs: 更新 README feature 表 + 升级指南 + 示例注释 + roadmap 同步

- README 添加 feature 组合表 + 模块级 features 清单 + 升级指南
- 18 个 example 顶部添加 Required features 注释
- roadmap.md 和 roadmap-v0.3.2.md 同步 Phase 26-27 完成状态
- cargo fmt 全量格式化（修复预存格式问题，CI format job 可通过）

src/llm/provider/anthropic.rs

@@ -18,7 +18,6 @@ use serde::{Deserialize, Serialize};
 use serde_json::{Value, json};
 use tracing::{debug, error, info, warn};
 
-use crate::llm::{LlmProvider, ProviderCapabilities, ProviderFeatures};
 use crate::llm::error::LlmError;
 use crate::llm::types::message::{ContentBlock, ContentBlockType, Message};
 use crate::llm::types::request_v2::MessageRequest;
@@ -26,6 +25,7 @@ use crate::llm::types::response_v2::{
     MessageResponse, PartialMessageResponse, PartialUsage, StopReason, StreamEvent,
 };
 use crate::llm::types::usage::Usage;
+use crate::llm::{LlmProvider, ProviderCapabilities, ProviderFeatures};
 
 /// Anthropic Provider 默认 `max_tokens` 兜底值。
 ///