fix(frontend): replace field-sizing:content with JS auto-resize to fix CJK cursor offset

[X33834]

Closes: #1224

Problem

TaskChatInputBox's textarea uses [field-sizing:content] (field-sizing: content). With full-width (CJK) characters the browser misrenders the caret, so the visible cursor drifts ~one full-width char to the right of the real insertion point (worst at line ends / after CJK text).

Root cause

field-sizing: content has known caret/selection rendering quirks for CJK text in the textarea. Notably, the other two task textareas in this repo already avoid it: create-default-task-dialog.tsx and start-develop-task-dialog.tsx both use field-sizing-fixed.

Fix

• Remove [field-sizing:content] from the task chat inputbox textarea.
• Keep the auto-grow behavior by syncing textarea.style.height from scrollHeight in an effect keyed on content (falls back to min-h-8 when empty, capped by max-h-36 + overflow-y-auto).

This preserves the auto-resizing UX while eliminating the CJK caret offset.

Verification

• eslint src/components/console/task/chat-inputbox.tsx — clean
• tsc -b — clean
• vite build --mode online — succeeds

[X33834]

友好 ping 一下 🙏 这个修复很小（+14/-1），解决中文输入时光标偏移的问题，方便时帮忙看一眼就好，不急～