add-ynd-commandlisted

# Add a `ynd` command `ynd` is half the product — 13 commands against `ynh`'s 31 — and it had no authoring guide while `add-vendor-adapter` covered the other half. Work the checklist in order. Each step is a place a command has actually been shipped incomplete. ## Before you start Read an existing command of the same shape rather than starting from a blank file. `cmd/ynd/compose.go` is the best model: it parses flags by hand, resolves its source from flag then env then positional, and supports `--format text|json` with a split renderer. ## 1. Decide the shape | Shape | Model to copy | Notes | |---|---|---| | Reads a harness, prints a report | `compose.go` | source resolution + `--format` | | Reads a harness, writes files | `preview.go`, `export.go` | needs `-o` and a destination guard | | Operates on loose files | `lint.go`, `fmt.go` | takes multiple positional paths | | Interactive | `inspect.go`, `compress.go` | needs prompt indirection — see step 6 | **Destructive commands have their own rules.** If the command deletes or overwrites anything, read `.claude/rules/destructive-operations.md` first. It is written from an incident and it is not optional. ## 2. Dispatch `cmd/ynd/main.go` — add a `case` to the switch: ```go case "mycommand": err = cmdMyCommand(os.Args[2:]) ``` Keep it alphabetical only if the neighbours are; match the file, do not reorganise it in the same change. ## 3. The command function, in two parts Split it so the output is testable without