feat: add ui line-wrap & code block css fixes

[perber]

No description provided.

[Copilot]

Pull request overview

Adds a line-wrap toggle to the markdown editor toolbar (persisted in localStorage) and applies CSS fixes around code-block scrolling, prose word-wrap, an active-toolbar-button modifier, and a mobile sidebar overlay z-index. Also renames stale .markdown-editor__preview-container selectors to .markdown-editor__preview and adds an e2e test for the new toggle.

Changes:

• New lineWrap setting in the editor Zustand store, wired into MarkdownCodeEditor via a CodeMirror Compartment and a new toolbar button.
• Code-block CSS: scroll moved from the wrapper onto the inner <pre>, copy actions repositioned, and break-words added to the three markdown surfaces.
• Selector rename markdown-editor__preview-container → markdown-editor__preview, sidebar overlay raised to z-20, and a new e2e test for the toggle.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
ui/leafwiki-ui/src/stores/editor.ts	Adds persisted lineWrap state and toggle action.
ui/leafwiki-ui/src/features/editor/MarkdownCodeEditor.tsx	Adds wrap/no-wrap CodeMirror extensions reconfigured via a compartment driven by the new prop.
ui/leafwiki-ui/src/features/editor/MarkdownEditor.tsx	Reads lineWrap from the store and forwards it to the code editor.
ui/leafwiki-ui/src/features/editor/MarkdownToolbar.tsx	Adds the line-wrap toolbar button and switches preview button to an active-modifier style.
ui/leafwiki-ui/src/features/preview/MarkdownCodeBlock.tsx	Removes custom-scrollbar from the outer wrapper now that scroll lives on the inner <pre>.
ui/leafwiki-ui/src/features/preview/markdownPreviewCodeTheme.css	Moves overflow-x to inner <pre>, repositions copy actions.
ui/leafwiki-ui/src/index.css	Adds --active button class, break-words on prose surfaces, z-index bump for mobile overlay, and selector renames.
e2e/tests/editor.spec.ts	Adds an e2e test verifying the line-wrap toggle.

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