Boards, step 4: the other panel types — bar, stacked area, number with sparkline, table, heat strip #1562

Part of #1557.

Done looks like:

• [ ] src/boards/chart.ts draws bar, stacked area (grouped series), single number with a sparkline, table, and heat strip (time x category) as SVG/HTML, every label escaped.
• [ ] /boards/data offers the chart type beside the query.
• [ ] Tests (in an existing boards test file, or a new one added to GATE in scripts/gate.ts): each type renders from the same seeded query with the expected element count.