include_cRQA silently ignores the flat list its schema documents as supported

[mikub97]

docs/contracts/config.schema.json defines one pairList and both include_cRQA and include_crosswavelet $ref it. Its own description says:

Either explicit pairs [[a,b],[a,c]], or a legacy flat list [a,b,c] which is expanded to all combinations. Both forms are supported; prefer pairs.

Cross-wavelet honours that. Cross-RQA does not: it skips every entry that is not a two-element list, finds no valid pairs, prints a warning and returns without writing a file. So a config that validates against the contract produces a cross-RQA tab with no data, and the only clue is a line in the build log.

"include_crosswavelet": ["a", "b", "c"],   // three pairs
"include_cRQA":         ["a", "b", "c"],   // nothing at all

Where

• packages/dims-analysis/dims_analysis/steps/crqa.py — valid_pairs()
• packages/dims-analysis/dims_analysis/steps/crosswavelet.py — the expansion, around the base_pairs construction
• docs/contracts/config.schema.json:13-34 — the shared pairList
• Already documented as a trap in docs/analyses/index.md, which is not the same as fixing it

What to do

Pick one and make all of it true. Either expand the flat form in crqa.py as cross-wavelet does — the combination logic is four lines and could be shared — or drop the legacy form everywhere: from both steps, from apps/builder/dims_builder/validate.py, from packages/dims-tabs/crosswavelet.js, and from the schema.

Expanding is the smaller change and keeps existing study configs working. Dropping is defensible too, but it is a breaking config change and needs a release note.

Acceptance

• "include_cRQA": ["a", "b", "c"] either produces three pairs or is refused with a message naming the fix. It does not silently produce nothing.
• Whatever is decided, the schema, both steps, the wizard's validator and the tab gate agree.
• A test in packages/dims-analysis/tests/ covers the flat form for both keys.
• The gotcha paragraph in docs/analyses/index.md is updated or removed.

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