[survey2ddi 2/6] Port normalize_responses: the LimeSurvey response-data path

Step 2 of 6 for the survey2ddi retirement. Plan: HANDOVER_SURVEY2DDI.md. Independent of the xlsform2ddi --data issue; both are needed before survey2ddi's CLIs can be deprecated.

The gap

lstsvToDdiXml emits metadata. buildDataCsv (#8) emits a data CSV from submissions keyed by bare question name or group/name path. Neither shape is what a LimeSurvey response export produces, so there is no LimeSurvey full-mode path in this library.

limesurvey2ddi/transform.py in CorrelAid/survey2ddi does the missing step — normalize_responses(variables, rows):

• Bracket subkeys. LimeSurvey exports a select_multiple as one column per subquestion, keyed with a bracket suffix. _match_choice(subkey, choices) maps that suffix back to the parsed choice code so it can line up with the <name>_<choice> DDI variable.
• The underscore quirk. _norm(name) strips underscores and lowercases, "mirrors LimeSurvey's export behaviour" — LimeSurvey mangles field names on export, so matching must be done on the normalized form.

Both are LimeSurvey-specific and belong nowhere near the Kobo path.

What to build

src/pipelines/lstsv2ddi/data.ts, mirroring how xlsform2ddi/data.ts sits beside variables.ts:

lstsvToDataCsv(tsv: string, responses: Record<string, unknown>[], options?): string

Simplest honest shape: a key-normalizing adapter that re-keys LimeSurvey rows onto DDI variable names, then delegates to the existing buildDataCsv — the RFC 4180 writing and the column plan are already correct and must not be duplicated. Do not widen readCell in xlsform2ddi/data.ts with LimeSurvey heuristics; the two platforms' quirks stay separate.

Then add --data / --data-out to the lstsv2ddi CLI command, same flags and semantics as the xlsform2ddi issue.

Verification

• Fixture-based unit test: a LimeSurvey response export (bracketed multi columns, underscore-mangled names) → correct 0/1 binaries and correct scalar columns
• Header order equals <var name=""> order of lstsvToDdiXml on the same TSV
• Byte-compare against Python normalize_responses + build_data_csv on one fixture, accounting for the known column-order divergence in the Python emitter (documented in the handover doc)
• tests/fixtures/lstsv/ in survey2ddi has three usable structure TSVs

Acceptance criteria

• Bracket-subkey → choice-code matching ported, with the _norm normalization
• lstsv2ddi --data writes a CSV whose header matches the XML
• LimeSurvey-specific keying lives in lstsv2ddi/, not in the shared emitter
• Kobo path behaviour unchanged (existing data.test.ts still green)

Start with HANDOVER_SURVEY2DDI.md, src/pipelines/lstsv2ddi/data.ts, the existing xlsform2ddi/data.ts and variables.ts, and survey2ddi's limesurvey2ddi/transform.py. Compare the fixture-based output with Python normalize_responses plus build_data_csv, then run the existing data tests and lstsv2ddi CLI checks. Done means bracketed and underscore-mangled LimeSurvey fields produce the expected CSV, with headers matching the XML and Kobo tests unchanged.