feat: support pasting file paths copied from file manager (fixes #529)

[wuxiangru915]

Description

This PR resolves #529 by supporting pasting file and folder paths directly into input fields when users copy files/folders from their OS file manager (Windows Explorer, macOS Finder, Linux file managers), and adds WSL Windows drive path mapping for Linux/WSL environments.

Changes

• lib/clipboard-paths.ts:
  • Implemented fileUriToPath: converts file:// URIs to native OS paths, handling Windows drive letters (file:///C:/...), Unix paths, percent-encoding/spaces (%20, Unicode characters), and UNC paths.
  • Implemented extractPathsFromClipboardData: extracts file paths from File.path (Electron/desktop runtimes), text/uri-list, Linux clipboard formats (x-special/nautilus-clipboard, x-special/gnome-copied-files, x-special/mate-copied-files, x-special/xfce4-copied-files, application/x-kde-cutselection), macOS clipboard formats (public.file-url, text/x-moz-url), and text/plain file URIs.
  • Implemented formatPathsForInput: formats single or multiple file paths with automatic quoting for paths containing whitespace.
• lib/paths.ts & lib/directory-browser.ts & app/api/cwd/validate/route.ts:
  • Added convertWindowsPathToWsl: automatically converts Windows drive paths (e.g. C:\Users\... or C:/...) to WSL mount paths (/mnt/c/Users/...) when running on Linux/WSL.
• components/DirectoryPicker.tsx:
  • Added onPaste handler to directory path input box to automatically paste copied file/folder paths.
• components/ChatInput.tsx:
  • Updated handlePaste so non-image files copied from file manager insert their formatted file paths directly into the message textarea.
• components/PluginsConfig.tsx:
  • Updated onPaste on the plugin source input to support pasting folder/package file paths.
• components/ChatWindow.tsx:
  • Updated extension custom panel paste handler to handle clipboard file paths.
• app/api/cwd/browse/route.ts:
  • When browsing a path that points to a file (e.g. pasted into DirectoryPicker), automatically navigates to its parent directory rather than failing.
• Tests:
  • Added unit test suite lib/clipboard-paths.test.mjs (12 tests), updated lib/directory-browser.test.mjs and lib/paths.test.mjs, and added components/DirectoryPicker.test.mjs.

Fixes #529.