[建议 / Feature] Find in document (Ctrl+F) for the built-in file preview #1262

提交前确认 · Pre-submission checklist

• 我已搜索过现有 issue，确认这不是重复提议 / I searched existing issues and confirmed this isn't a duplicate.
• 我已阅读 CONTRIBUTING.md / I've read CONTRIBUTING.md.

问题类别 · Category

UI / 界面体验 · UI / UX

涉及的 Agent 框架 · Agent framework

ZCode Agent（自研）

使用场景 · Use case

Reading a long document in ZCode's built-in preview (a 2,000-line Markdown report or architecture doc — the exact kind of document ZCode agents produce), there is no way to search inside it: Ctrl+F does nothing, and since the preview is a custom renderer there is no browser find to fall back on. Looking for a specific term, class name or error message means scrolling and eyeballing the whole document — the opposite of what a document viewer is for.

建议方案 · Proposal

Add standard find-in-document to the preview panel:

• Ctrl+F / Cmd+F opens a search bar scoped to the preview; Enter / F3 jumps to the next match, Shift+Enter to the previous, Esc closes.
• All matches highlighted at once, the current match distinctly; a match counter (n / N); scroll follows the active match.
• Options: case-sensitive, whole word, regular expression.
• Coverage: Markdown preview first; extend to the other built-in viewers that don't already provide their own search (docx / xlsx / pdf as applicable).
• Nice to have: highlight matches in the TOC/outline pane requested in [建议 / Feature] Table of contents / outline pane in the built-in Markdown viewer (button toggle or automatic right sidebar) #1240, so repeated matches are visible in the document structure at a glance.

预期价值 · Expected value

Find-in-document is a baseline expectation for any document reader (VS Code preview, browser PDF viewer, Typora all have it). It makes the growing preview surface (#1239 PlantUML, #1240 outline) genuinely usable for the long technical documents ZCode itself generates.

你认为的优先级 · Your perceived priority

中 · Medium

你使用的 ZCode 版本 / 环境 · ZCode version / environment

ZCode desktop app 3.16.3, Windows 11

补充材料 · Additional context

Same preview-family requests: #1240 (TOC/outline pane), #1239 (PlantUML rendering), #1008 (refresh action). Related but broader: #178 ("Office Mode" document workspace).