fix(asr): surface Volcengine 403 as 'credentials rejected'

[appergb]

User description

Summary

用户反馈日志（openless-2026-05-15T01-12-07.log）显示 9 次连续：
```
[coord] open ASR session failed: connection failed: HTTP error: 403 Forbidden
```

诊断：HTTP 403 是 Volcengine bigmodel ASR 在 WebSocket 握手阶段返回的，网络通到了 Volcengine 服务器（不然不会有 HTTP 状态码），但服务端拒绝。这是凭据问题（App ID / Access Token 错、Resource ID 错、或账号没开通 SAUC bigmodel 资源），不是网络 / 代码 bug。

但当前 capsule 显示原始 HTTP error: 403 Forbidden，普通用户不会读 → 反馈到客服。

改动

`volcengine.rs`：

• 加 `VolcengineASRError::AuthRejected(u16)` variant，display 是中文具体引导
• 加 `classify_connect_error()` 函数：tokio-tungstenite 握手返回 `Error::Http` 且 status ∈ {401, 403} 时归入 AuthRejected，其它握手错误（DNS / TLS / connection refused）仍走 ConnectionFailed 不变

用户看到的新文案：

Volcengine 凭据被拒（HTTP 403）：请检查 Settings → 凭据 → Volcengine 的 App ID 和 Access Token，或确认账号已开通 SAUC bigmodel 资源

Test plan

• `cargo test --lib` → 258 全过
• 手工验证：故意填错 Volcengine App ID → 录一段 → 看 capsule 显示新中文文案
• 手工验证：正确凭据 → 录音正常，不被误判为 AuthRejected
• 手工验证：断网 → capsule 仍显示原来的 `connection failed: ...` 不被这次改动污染

不发 tag

按 hotfix 计划，merge 到 beta 后不发 `v1.3.2-3-beta-tauri` tag，下一个 Beta 一起出去。

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PR Type

Bug fix

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Description

• Classify Volcengine 401/403 handshakes

• Surface credential rejections as AuthRejected

• Keep other connect failures unchanged

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Diagram Walkthrough

flowchart LR
  A["connect_async handshake error"] -- "HTTP 401/403" --> B["AuthRejected(status)"]
  A -- "other errors" --> C["ConnectionFailed"]
  B -- "capsule text" --> D["凭据被拒（403）"]
  C -- "capsule text" --> E["connection failed: ..."]

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File Walkthrough

	Relevant files
Bug fix	volcengine.rs Classify Volcengine handshake credential errors                    openless-all/app/src-tauri/src/asr/volcengine.rs Adds AuthRejected(u16) for 401/403 handshake responses Replaces direct connect_async error mapping with classify_connect_error Keeps DNS, TLS, and network failures as ConnectionFailed Documents why credential rejections are handled separately +21/-3

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[github-actions]

PR Reviewer Guide 🔍

(Review updated until commit 1234dcd)

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[github-actions]

Persistent review updated to latest commit 1234dcd