feat(reports): support composable mix-and-match data functions per canned report

[thecaffiend]

Background

A canned report is tied to exactly one data function today. Config carries a single data_function block, _create_canned_report (capeinfra/meta/capemeta.py) builds one Lambda and stores its ARN under the scalar data_function key in the canned-report DDB table, and get_canned_report (assets/api/capi/handlers/get_canned_report.py) invokes that one ARN and renders its returned dict.

The report payload shape is already flexible (a free-form dict passed straight to the template), so a single function can return many query results. But we want to be able to compose a report from a collection of small, independently maintained data functions. Small composable functions also fit Lambda's default per-invocation timeout better than one function running many queries serially.

Scope

• Config schema: allow a report to declare a list of data functions instead of a single data_function.
• capemeta.py: build N Lambdas per report and persist N ARNs; the stored canned-report meta currently uses a scalar data_function field.
• Canned-report DDB contract + capepy: CannedReportTable.get_report reads the scalar data_function; storing/reading a list likely requires a capepy change or a new field.
• Handler: get_canned_report must invoke each data function and merge payloads with a namespacing scheme to avoid key collisions.
• Invocation model: invoke the data functions concurrently to actually realize the timeout benefit; serial invocation of N small Lambdas is slower and costlier than one Lambda running N queries.

Notes

• Surfaced while scaffolding feat(seqauto): add new raw result etl and update report to show data from it #363. That branch takes the low-churn path of folding the new caerbannog queries into the existing single bactopia data function; the merged-dict payload it produces is the same shape this composable model would assemble, so the template work carries forward.

Refs #363