修复流式 SSE UTF-8 切分与部分输入丢失

[H-Chris233]

User description

变更说明

• 修复 OpenAI-compatible 流式润色、QA 流式、Codex OAuth 流式 SSE 在 HTTP chunk 中切开 UTF-8 多字节字符时误报 non-utf8 的问题。
• type_unicode_chunk 改为返回已确认输入字符数；中途失败时只记录已实际落屏前缀，保证 history / clipboard / 屏幕内容一致。
• 流式已落屏文本跳过最终简繁收敛与纠正规则，避免后处理改写用户屏幕上已经出现的内容。
• Linux enigo 路径改为逐字符输入，失败时也尽量报告 partial typed chars。

Closes #413

验证

• cargo test --manifest-path src-tauri/Cargo.toml --lib
• cargo check --manifest-path src-tauri/Cargo.toml
• git diff --check

---

PR Type

Bug fix, Enhancement, Tests

---

Description

• Fix UTF-8 multi-byte splitting across HTTP chunks by incremental decoding in streaming polish/QA/Codex

• Return typed character count from type_unicode_chunk to prevent history/clipboard mismatch on partial failure

• Skip Chinese script convergence and correction rules for already-streamed text to avoid rewriting displayed content

• Add comprehensive tests for UTF-8 edge cases and partial typing recovery

---

File Walkthrough

	Relevant files
Bug fix	dictation.rs Streamed text consistency and post-processing bypass          openless-all/app/src-tauri/src/coordinator/dictation.rs Add append_typed_prefix() and finalize_dictation_text() helpers Use typed_chars from type_unicode_chunk to record only confirmed prefix Skip mutating post-processing for streamed text to preserve on-screen content Add unit tests for prefix truncation and post-processing bypass +135/-43 polish.rs Incremental UTF-8 decoding for SSE streaming endpoints      openless-all/app/src-tauri/src/polish.rs Introduce utf8_pending buffer and append_utf8_sse_chunk() for incremental decoding Replace direct from_utf8() calls in three streaming methods Add finish_utf8_sse_chunks() to validate final pending bytes Add integration tests simulating split UTF-8 across HTTP chunks +220/-16
Enhancement	unicode_keystroke.rs Return typed char count on partial keystroke failure          openless-all/app/src-tauri/src/unicode_keystroke.rs Change type_unicode_chunk return type to Result Add TypeError::Partial variant carrying successfully typed char count Implement per-character accounting on macOS, Windows, and Linux Add tests for Partial error reporting +127/-22

---

[github-actions]

PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

🎫 Ticket compliance analysis ✅ 413 - Fully compliant Compliant requirements: UTF-8 chunk 切分兼容：流式润色、QA 流式、Codex OAuth 流式均已支持。 部分输入成功时仅记录已输入前缀，避免 history / clipboard 与屏幕不一致。 已流式显示文本跳过最终后处理。 已补充相关回归测试。

⏱️ Estimated effort to review: 3 🔵🔵🔵⚪⚪

🧪 PR contains tests

🔒 No security concerns identified

⚡ No major issues detected