Pull request to merge the changes from version 1.0.1

[shinya]

Summary

This release adds two quality-of-life features — a copy button on preview code blocks and a drag-resizable vertical tab sidebar — and makes HTML/PDF exports default to the source
document's filename. It also bumps the version to 1.0.1 with the corresponding What's New entries and changelog.

Changes

• Copy button on code blocks: Code blocks in the preview now show a copy button. Copying goes through the Tauri clipboard plugin (with a browser-API fallback), uses event
  delegation so the listener survives dangerouslySetInnerHTML swaps, and shows a transient check-mark feedback. Added the clipboard-manager:allow-write-text capability and
  localized tooltips in all 14 languages.
• Adjustable vertical tab width: The vertical tab sidebar can be resized by dragging its edge (clamped to 180–480px). The width is persisted as a new
  interface.tabSidebarWidth setting with debounced writes, and dragging below the collapse threshold unpins the sidebar back to auto-hide.
• Export filename from source document: HTML and PDF exports now derive the save dialog's default filename from the document being edited via a new deriveExportFileName
  utility (markdown extension swapped for the target one); unsaved documents keep the legacy markdown-export fallback. (Use the source document name as the default export filename #442)
• Version bump to 1.0.1: Updated version files, build scripts, whatsNew.ts, the whatsNew.changes entries in all 14 locales, and CHANGELOG.md. Aligned "vertical tab"
  terminology with the settings screen across locales (e.g. ja 垂直タブ, ko 수직 탭, zh-CN 垂直标签页).
• Added copy-button scenarios to the monkey test cases (en/ja).

Tests

• previewHtmlProcessing.test.ts / Preview.test.tsx: new tests for copy-button injection into rendered code blocks and the copy interaction (clipboard call, feedback state).
• pathUtils.test.ts: new tests for deriveExportFileName (markdown extension swap, non-markdown extensions, unsaved fallback).
• useSettings.test.ts / AppContent.test.tsx: new tests for tabSidebarWidth persistence, clamping, and the sidebar drag/unpin behavior.
• desktopApi.test.ts: coverage for the defaultName parameter of the HTML save dialog.