Emit per-track summary `console.warn` for missing `dataTooltip` field references

[dlrice]

Context
After the first render pass, a single summary console.warn lists all missing fields for that track, not per data point. src/tooltips/resolve.ts silently substitutes missing fields as empty strings (which is correct behaviour at the per-cell level), but authors get no feedback when a dataTooltip template references a field the adapter never produced. This is a common foot-gun when authoring against an unfamiliar data source: the tooltip renders blank cells and the author has no breadcrumbs to the cause.

Task
Implement a per-track missing-field accumulator in the tooltip resolver and emit one summary console.warn per track, not per data point.

Scope:

• In src/tooltips/resolve.ts (or a helper), track the set of field paths that resolved to undefined while rendering any tooltip on a given track during a render pass.
• After the render pass completes (or on the next animation frame — whichever is cheaper), emit a single console.warn of the form: "[protvista-uniprot] Track <categoryId>/<trackId>: dataTooltip references unknown fields: <field>, <field>, …". The warning fires once per track per render pass, not per data point.
• Don't warn when the field resolves to a legitimate empty string / null — only when the field path doesn't exist on any of the track's data points.
• Integrate the accumulator with both kind: fields and kind: markdown authoring forms.
• Add a unit test in src/tooltips/__spec__/resolve.spec.ts that: (a) renders a tooltip template referencing three unknown fields across ten data points, and (b) asserts console.warn was called exactly once with all three field names.
• Reinstate the deleted spec material in specs/config-approach.md: the Edge Cases row and the acceptance criterion.

Notes:
Keep the allocation/accounting path on the hot render path cheap — a per-track Set<string> populated during field resolution, flushed once per render pass, should be sufficient. No observable behaviour change for correctly-authored configs.