[survey2ddi 6/6] Docs: pull commands, the LimeSurvey data path, and survey2ddi's new scope

Step 6 of 6 for the survey2ddi retirement. Plan: HANDOVER_SURVEY2DDI.md. Do this last — after the CLI, both pull adapters, and the parity work have landed.

What to update

• README.md — the Quick Start CLI block lists four conversion commands; add the Kobo and LimeSurvey pull/transform commands. The ecosystem table's "Consumed by" column should reflect that direct CLI use now covers the pull paths too.
• src/pipelines/README.md — the "The DDI data file" section documents the XLSForm response path and the column-order contract. Add the LimeSurvey response path (bracket subkeys, the _norm export quirk) once that port lands, and say which module owns which platform's keying.
• ARCHITECTURE.md — the pull adapters are a new layer: node-only, network-touching, deliberately outside the browser entry. Record that boundary where the existing cli.ts / fileChoices.ts exclusions are described.
• Anywhere survey2ddi is named — its scope becomes the DDI read side (read_variable_labels, read_value_maps, apply_value_labels for labelling a dataframe). It is no longer a converter. Do not describe it as deprecated wholesale; the reader is staying.

Acceptance criteria

• npm run validate green (markdownlint + prettier are part of it)
• Every documented command exists and its --help matches the docs
• No doc still presents survey2ddi as a conversion tool

Read HANDOVER_SURVEY2DDI.md first, then inspect README.md, src/pipelines/README.md, and ARCHITECTURE.md alongside the completed CLI, pull adapters, and parity work. Update the named sections and every survey2ddi reference, then run npm run validate and verify that each documented command exists, its --help matches, and no documentation presents survey2ddi as a conversion tool.