feat: edit forwarded ports individually

[dr-hoseyn]

Summary

• add dedicated actions to add, edit, or remove one forwarded-port entry
• show the current entry as the default while editing, so the rest of the list does not need to be re-entered
• keep full-list replacement available for bulk changes
• keep hidden Telegram/SOCKS relay mappings preserved through the existing EditTunnel path
• validate individual edits before saving and prevent removal of the last forwarded port

Testing

• gofmt on changed Go files
• GOOS=linux GOARCH=amd64 go test -c ./internal/manage
• added unit coverage for add/edit/remove and invalid inputs

Note: current main already contains config hot reload in cmd/reload.go; this PR addresses the remaining CLI usability issue where changing one forwarded port required retyping the entire list.