fix(frontend): drop empty/control-char auth headers (#1000) (#1003)

Stale localStorage credentials (`jwt` / `auth` / `adminAuth` / `userJwt` /
`access_token`) can be the empty string, the literal string `"undefined"`,
or carry a stray newline / control character left over from an older
build. axios + undici reject these eagerly with `Invalid character in
header content ["Authorization"]`, so every API call crashes client-side
before reaching the worker.

This adds two tiny helpers in `frontend/src/utils/headers.js`:

- `safeHeaderValue(v)` returns the trimmed value when it is a non-empty
  string with no control chars (per RFC 7230) and no `"undefined"` /
  `"null"` sentinel; otherwise `undefined`.
- `safeBearerHeader(jwt)` wraps a safe JWT with `Bearer `, otherwise
  `undefined`.

`apiFetch` builds the headers object incrementally and only sets each
auth header when its value is safe. Missing/unsafe credentials now drop
out cleanly and the worker returns a normal 401, which the existing
`response.status === 401` flow already handles by surfacing the auth
prompt — the same UX users see on a fresh session.

Tests: `frontend/src/utils/__tests__/headers.test.js` adds 9 vitest
cases covering safe input, sentinel strings, control chars (\\n / \\r /
\\t / NUL / 0x1F / DEL), trimming, and `Bearer` construction. Build
(`pnpm build`) and tests (`pnpm test`) both pass.

Co-authored-by: voidborne-d <voidborne.d@agentmail.to>
Co-authored-by: Dream Hunter <dreamhunter2333@gmail.com>

CHANGELOG.md

@@ -19,6 +19,7 @@
 
 - fix: |Frontend| 收窄地址管理相关弹窗宽度，并让地址表格在弹窗内部横向滚动，避免多地址场景撑宽弹窗
 - fix: |Frontend| 修复 `/open_api/settings` 未返回 `domains` 数组时前端设置初始化直接调用 `map()` 报 `undefined` 错误的问题，统一按空数组兜底处理
+- fix: |Frontend| 修复前端在 `jwt` / `auth` / `adminAuth` 等 localStorage 凭据为空字符串、字面量 `"undefined"` 或包含换行/控制符时，请求构造的 `Authorization` 等头部抛出 `Invalid character in header content` 导致前端所有接口报错的问题（issue #1000）。新增 `safeHeaderValue` / `safeBearerHeader` 工具，对全部认证头做 RFC 7230 校验，不安全的值直接跳过该头部，让 worker 走标准 401 而不是请求级崩溃
 
 ### Improvements