feat(signals): non-time plot widget, multi-axis normalization, export modal

[jacobjurek]

Summary

Three enhancements to the Signals page, built as independent workstreams.

1. Multi-axis normalization fix (QueryChart.tsx)

When traces span multiple axis groups, only the first group's y-axis was drawn. Now every group renders: group 1 on the left (pixel-identical for single-group queries), additional groups on the right with stepped offsets, each axis color-matched to its traces. The grid margin grows dynamically so labels never clip. The hidden normalized [0,1] axis and tooltip true-value recovery are unchanged.

2. Export modal (ExportDialog.tsx, export.ts, SignalWidget.tsx)

The two bare CSV/PNG icon-buttons are replaced by a single Export dialog offering:

• PNG — background (light / dark / transparent) + scale (1x–4x) + filename
• Data — CSV and JSON, with an include hidden traces toggle
• Copy image to clipboard (with toast)

Export logic stays as pure functions in lib/export.ts.

3. Custom non-time plot widget (PlotWidget/PlotChart, lib/pairs.ts, backend /query/pairs)

A new plot widget sits alongside the time-series widget ("Add plot"), supporting:

• XY scatter and connected-line/path (e.g. GPS lat vs lng track), with optional color-by
• bar / pie of grouped aggregates (reuse existing /query/run)
• 3D scatter (adds echarts-gl)

New POST /query/pairs endpoint returns timestamp-aligned paired samples via the query_signals() + merge_signals() (merge_asof) helpers. Response is the bare {columns, rows} body (gateway adds the {data:...} envelope).

Notes

• This PR includes the previously-untracked backend helpers query/query/service/query.py and query/query/model/query.py because the new /query/pairs route imports them; and SignalTree.tsx, used by PlotWidget.
• echarts-gl registered via its tree-shakeable install modules (its ESM entrypoints are broken upstream); ambient types in echarts-gl.d.ts.

Verification

• Dashboard tsc --noEmit clean; npm run build succeeds.
• Backend route verified end-to-end: POST /query/pairs → 200 with {columns, rows} real merge-aligned ClickHouse data, reachable through the kerbecs gateway.
• Full Docker stack rebuilt and confirmed: all 11 containers running, dashboard serving, echarts-gl present in the container.

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