TMB_DIGIT_SYMBOL_MATCHING: only has the 6-symbol layout, and still shows a red selection outline #42

A clinical collaborator compared our TMB_DIGIT_SYMBOL_MATCHING implementation against the paper/BHOP version of the same task and found two remaining differences (a third — missing touchscreen support — was checked and is already handled correctly, so it's not included here):

1. Only the 6-item layout exists; BHOP/PECS uses a 9-item single-row layout

lib/interactive/TMB_DIGIT_SYMBOL_MATCHING/fragment.html and render.js hard-fix the task at 6 symbols, arranged as two stacked rows of 3 (#keyRow1/#keyRow2, and symbols = moresymbols ? range(1,30).shuffle().slice(0,6) : [1,2,3,4,5,6] — always 6, regardless of the moresymbols param). The published TMB version used at BHOP/PECS instead uses 9 symbols in a single vertical row. Differences in the number of available symbols and layout could affect performance comparisons between sites.

Our collaborator has supplied reference materials for the 9-item version and confirmed there's budget to build it. Given that changing the existing instrument in place would make already-collected 6-item data non-comparable, this is probably best built as a new sibling instrument (e.g. TMB_DIGIT_SYMBOL_MATCHING_9) rather than modified in place — but that's a call for whoever picks this up.

2. Selected response still shows a red outline

styles.css still has .responseHighlight { border: 5px solid red; }, applied via tmbUI.highlight = 'responseHighlight' in render.js / TestHelper.v1.Oct23.js when a response is selected. BHOP's version has no such outline. For task parity this should be removed (or replaced with something more subtle) — small CSS change, but worth bundling with whichever version of the instrument (existing or new 9-item one) actually ships, rather than fixing twice.

Downstream reference: DouglasNeuroInformatics/CPPQ#100