fix(metadata,cli,frontend): drop unnamed columns in the shared builder (#109)

[Mandyx22]

What

Re-cut of finding #2 of #109, layered on #103's shared buildPsychDSDataFiles. Supersedes #112 and #113.

R's write.csv (default row.names = TRUE) prepends an unnamed row-index column, so the CSV header starts with a bare comma — an empty-string column name. It can't appear in variableMeasured (Psych-DS requires a name), so generate() drops it from the metadata, but the on-disk CSV kept it → validation failed with CSV_COLUMN_MISSING_FROM_METADATA.

How

The strip lives in the shared data-file path so the CLI and frontend behave identically by construction (no per-caller helper):

• New exported stripUnnamedColumns helper.
• generate() strips empty/whitespace-only columns from the parsed data up front, with a single warning instead of per-row spam — keeps variableMeasured clean and standalone library use safe.
• buildPsychDSDataFiles strips the main table before emitting it: a clean CSV keeps its exact bytes (verbatim mainContent); a file with an unnamed column is re-serialised from the cleaned rows. Sidecars are already clean (they come from generate()'s stripped extraction).
• Both callers feed parsed mainRows: the CLI (rename-plan and non-plan write paths) and the frontend runGenerate now parseCSV the CSV input, so the written / zipped / in-browser-validated CSV always matches the metadata.

This replaces #112's CLI verbatim-write rewrite and #113's frontend-only normalizeData.ts with one shared-builder implementation.

Testing

• Full suites green: metadata 148, CLI 127, frontend 37.
• New coverage: stripUnnamedColumns unit; buildPsychDSDataFiles (dirty CSV re-serialised, clean CSV byte-for-byte, JSON rows); generate() strip (one warning, not per-row); CLI processDirectory on both write paths; frontend runGenerate parse→build path.
• tsc --noEmit clean; no new eslint any introduced.
• End-to-end (built CLI) on an R-style fixture ,subject_id,trial_type,trial_index,rt,response: written header drops the empty column and matches variableMeasured; no CSV_COLUMN_MISSING_FROM_METADATA. (The residual time_elapsed error is finding Incorporating Psych-DS validator with the metadata module #1 / fix(metadata): register jsPsych system variables lazily (#109) #110, not on this branch.)

⚠️ Stacked PR

Targets fix/frontend-missing-datafile (#103), not main, because it builds on buildPsychDSDataFiles. Merge #103 first, then re-target this to main.

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🦋 Changeset detected

Latest commit: 840dc2b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@jspsych/metadata	Patch
@jspsych/metadata-cli	Patch
frontend	Patch

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