Add rich preview support for three new file categories by leveraging
external CLI tools with graceful fallback when tools are missing.
- PDF: text extraction via pdftotext, page count via pdfinfo
- Audio: metadata via ffprobe (duration, bitrate, codec, sample rate, channels)
- Video: metadata via ffprobe (duration, bitrate, video/audio codec, resolution)
- New PreviewKind constants: PDF, Audio, Video
- New Metadata fields for extended preview data
- New extension maps and Category() entries for pdf/audio/video
- Icons: PDF (), audio (), video () in preview header
Closes#5
Expand textExtensions with many missing common text file extensions
(.lua, .rb, .vue, .svelte, .dart, .tex, .scala, .lisp, and many more).
Add textFilenames list for well-known text files without a meaningful
extension (Makefile, Dockerfile, README, LICENSE, .gitignore, etc.)
so they open in the editor via handleEdit() instead of falling back
to xdg-open via handleOpenExternal().
