[Feature]: 支援在 .env 檔案配置 openrouter / claude code 環境變數

[bibbychan]

Issue Type

• ✨ feature - New feature (non-breaking change which adds functionality)
• ⚡ performance - Performance improvement
• 🖥️ backend - Backend-related feature
• 🎨 frontend - Frontend-related feature

Component Scope

Both Frontend and Backend

Problem Statement

目前 claude-code-webui 並未原生支援從 .env 檔案載入 openrouter 或 Claude Code API 相關的環境變數，導致每次環境部署、開發、或切換 API Provider 時，需手動在程式碼或配置中更改，影響自動化與多環境管理效率。

Proposed Solution

希望能實作自動讀取 .env 檔案內容，並把 openrouter/Claude Code 相關（如 OPENROUTER_API_BASE, CLAUDE_CODE_API_KEY 等）環境變數注入到系統，讓專案部署、測試、切換 Provider 時能更彈性且安全管理。

Use Cases

• 多人協作或 CI/CD 部署自動化時方便切換、保護敏感金鑰
• 測試、開發不同 API 平台時只需切換 .env 檔案，不需動程式碼
• 支援多 Provider 或多專案時大幅降低配置複雜度

Alternatives Considered

• 直接編輯設定檔或硬編碼（安全性低且不易管理）
• 使用系統環境變數（但部分服務難以跨平台且可見性差）

Priority

Low - Nice to have

Implementation Complexity (if known)

None

Implementation Considerations

• 建議可用 dotenv 套件讀取 .env
• 需確認已有的配置讀取邏輯是否衝突，並妥善 fallback
• 可考慮 error handling，避免遺漏重要環境變數時出錯

Examples or Mockups

.env 檔範例

OPENROUTER_API_BASE=https://api.openrouter.ai/v1
CLAUDE_CODE_API_KEY=your_claude_key_here

Contribution

• I would be willing to implement this feature myself
• I would be willing to help test this feature
• I would be willing to help with documentation
• I would be willing to provide feedback during development

Additional Context

參考 dotenv 實作與安全配置最佳實踐

Checklist

• I have searched existing issues and feature requests to make sure this is not a duplicate
• I have provided a clear problem statement and proposed solution
• I understand that feature requests are prioritized based on community needs and maintainer capacity