[survey2ddi 3/6] Kobo pull adapter + formtransform kobo command

Step 3 of 6 for the survey2ddi retirement. Plan: HANDOVER_SURVEY2DDI.md. Best done after the xlsform2ddi --data issue, since kobo transform composes it.

Why

kobo2ddi in CorrelAid/survey2ddi is the only way to go from a Kobo asset UID to a codebook in one step. Its converter half is now duplicated here; its fetch half has no equivalent. Porting the fetch half is what lets that package stop shipping a second DDI implementation.

What to port

kobo2ddi/client.py — 98 lines of httpx, all straightforwardly fetch:

CLI surface mirroring the Python one:

formtransform kobo list
formtransform kobo pull <uid> -o output/
formtransform kobo transform <uid> -o output/     # pull + xlsform2ddi + data CSV

• Auth: --token, else KOBO_API_TOKEN. Server: --server-url, else KOBO_SERVER_URL, else https://eu.kobotoolbox.org. Keep the env var names identical so existing .env files keep working; node --env-file replaces python-dotenv, no dependency needed.
• Kobo submission records are keyed group/name with space-joined select_multiple values — exactly what buildDataCsv's readCell already handles, so transform is pull + the existing emitters with no adapter.

Constraints

• Node-only, like src/cli.ts and src/fileChoices.ts. Do not re-export the client from src/index.ts. The app must not start shipping an HTTP client, and a node:fs / network import surfacing in the browser bundle is a regression.
• Fail loudly on a missing token rather than issuing an unauthenticated request.
• Do not print the token in error messages or verbose output.

Acceptance criteria

• list / pull / transform behave as the Python CLI does, same env var names
• Pagination handled for assets and submissions (a >1-page asset is the test that matters)
• transform produces XML + CSV with a correct caseQnty
• Browser entry unchanged — nothing new reachable from src/index.ts
• --help for the command group and each subcommand

Start with HANDOVER_SURVEY2DDI.md and the Node-only entry points src/cli.ts and src/fileChoices.ts, then compare the requested behavior with survey2ddi's kobo2ddi/client.py. Verify list, pull, and transform help output, pagination, environment variables, XML and CSV output including caseQnty, and that src/index.ts and the browser entry remain unchanged.