Upload any file from the key bar beside the image button

[dibin666]

What

A paperclip button next to the key bar's image upload button sends any file (up to 3 MB) to the workstation. The host saves it and the path is pasted into the terminal, just like an image upload.

How

• Protocol: paste_file now also accepts mime: "application/octet-stream" with a name. New shared PASTE_FILE_MIME and sanitizePasteFileName (no directories, no leading dots, only letters/digits/._-, at most 120 chars, extension kept). New capability paste_any_file.
• Relay: sanitizes the name, skips magic-byte sniffing for files, and answers paste_file_host_outdated when the host doesn't advertise paste_any_file, so the whole payload isn't sent to a host that would reject it.
• Host: saves files as <uuid>-<sanitized name> (0600, same pinned dir, size cap and pruning). The name is sanitized again on the host.
• Web: new UploadButton (image / file kinds), a hidden picker that accepts any type, and uploadFile in the upload hook. Files over the limit are refused before reading. Only the button that started an upload shows the percentage.
• i18n (en/zh), docs/protocol.md, README (en/zh).

Tests

• relay: a file is forwarded with its sanitized name; a file sent to an old host is refused.
• cli: a file is saved under its UUID and sanitized name without sniffing; the name sanitizer; the size cap.
• web: button placement/icon/labels, an any-type picker, viewer mode, a successful send and path paste, an oversize file refused, the outdated-host error.

npm run check and npm test pass.