Support Multiple Clipboard Content Types (HTML, Images, Files, etc.)

## Description

Currently, the clipboard manager captures only plain text (`text/plain`, e.g., `std::string`). However, modern clipboards often contain rich content such as HTML, images, or file paths. To make the tool more powerful and user-friendly, we should extend support to additional clipboard formats.

## Tasks

- [ ] Detect and log available MIME types in the clipboard (e.g., via `xclip -t TARGETS`)
- [ ] Add support for `text/html` (capture raw HTML snippets)
- [ ] Add support for images (`image/png`, `image/jpeg`)
- [ ] Add support for file paths (`x-special/gnome-copied-files`, `application/x-kde-cutselection`)
- [ ] Provide metadata for each entry in history (type, size, timestamp)
- [ ] Add CLI options to filter by content type (e.g., `hcp list --type image`)
- [ ] Add graceful fallback if content type is unsupported
- [ ] (Optional) Store non-text content in a separate storage folder

## Notes

- On Linux (X11), tools like `xclip`, `xsel`, and `wl-clipboard` can be used to probe the clipboard's contents.
- MIME types of interest include:
- `text/plain`
- `text/html`
- `image/png`
- `image/jpeg`
- `application/octet-stream` (for binary)
- `x-special/gnome-copied-files` (for file drag-and-drop)

## References

- [XClip MIME Type Targets](https://linux.die.net/man/1/xclip)