docs(readme): 用项目品牌图标替换 README H1 的 ⚡ 占位符;

- 新增 assets/logo.svg：从 favicon 单一事实源 _FAVICON_SVG（dashboard.py）派生，
  确保与线上 /favicon.svg 逐字符一致（青绿渐变 >_ prompt 笔划 + 通透圆环）；
- README.md 与 docs/zh-CN/README.md 双语 H1 以 <img> 引用该图标，采用
  width/height=32 + align="absmiddle" 适配 GitHub 净化器（保尺寸生效、与文案垂直居中）；
- 架构图 Mermaid 子图标签由 "⚡ coding-proxy" 改为纯文字 "coding-proxy"，与去 emoji 的 H1 统一。

🤖 Generated with [Claude Code](https://github.com/claude), [CodeX](https://openai.com), [Gemini](https://github.com/apps/gemini-code-assist)
Co-Authored-By: Aurelius Huang<threefish.ai@gmail.com>

Author: ThreeFish-AI

README.md

@@ -2,7 +2,7 @@
 
 <div align="center">
 
-# ⚡ coding-proxy
+# <img src="assets/logo.svg" alt="coding-proxy" width="32" height="32" align="absmiddle"> coding-proxy
 
 **A High-Availability, Transparent, and Smart Multi-Vendor Proxy for Claude Code**
 
@@ -125,7 +125,7 @@ graph RL
 
     Client["💻<br/>Client (Claude Code)"]:::client
 
-    subgraph CodingProxy["⚡ coding-proxy"]
+    subgraph CodingProxy["coding-proxy"]
         direction RL
 
         Router["RequestRouter<br/><code>routing/router.py</code>"]:::router

assets/logo.svg

@@ -2,7 +2,7 @@
 
 <div align="center">
 
-# ⚡ coding-proxy
+# <img src="../../assets/logo.svg" alt="coding-proxy" width="32" height="32" align="absmiddle"> coding-proxy
 
 **面向 Claude Code 的多供应商高可用透明智能代理**
 
@@ -125,7 +125,7 @@ graph RL
 
     Client["💻<br/>Client (Claude Code)"]:::client
 
-    subgraph CodingProxy["⚡ coding-proxy"]
+    subgraph CodingProxy["coding-proxy"]
         direction RL
 
         Router["RequestRouter<br/><code>routing/router.py</code>"]:::router