Support arbitrary file transfer in remote Herdr workflow

[barbatdev]

Context\n\nHerdr remote image paste works for screenshots/images: from macOS/Ghostty using hremote <host>, copying a screenshot/image and pressing Ctrl+V in the remote pane uploads a temp file remotely and pastes the path.\n\nArbitrary files from Finder/clipboard do not work in that flow. This is still a gap for PDFs, documents, logs, archives, etc.\n\n## Goal\n\nFind and implement a low-friction workflow for sending arbitrary local files from macOS to the remote Herdr/SSH workspace without leaving the terminal momentum.\n\n## Options to Evaluate\n\n- trzsz / tssh for terminal-native file transfer.\n- Minimal rput <host> <file...> [remote-dir] fallback using rsync.\n- Herdr upstream feature request for file clipboard/drop support beyond image clipboard.\n- Ghostty/iTerm2/Kitty-specific protocols if they fit the current stack.\n\n## Constraints\n\n- Do not require moving the whole workflow back to local Mac.\n- Preserve hremote as the primary flow.\n- Avoid a folder-sync inbox as the main UX; too much momentum cost.\n- Keep image paste via Herdr native Ctrl+V documented separately.\n\n## Acceptance Criteria\n\n- User can send a local file to the remote environment with minimal context switch.\n- Remote path is clearly printed/pasted for the active agent/session.\n- Works with filenames containing spaces.\n- Has a safe default destination such as ~/Incoming/cortex/....\n- Does not auto-upload sensitive files without explicit user action.