Related Issue

Resolve #186

Summary

• Adds 2D smooth-line support for line charts.
• Exposes the feature through CLI, --chart overrides, and the UI settings panel.
• Keeps smooth lines unavailable for 3D line charts and non-line chart types.

Changes

• Added line-only --smooth CLI flag and smooth line config field.
• Added --chart line:smooth support via the chart flag registry.
• Added Smooth lines UI toggle for 2D line charts.
• Hid the UI toggle when the line chart renders in 3D mode.
• Applied smooth: true to grouped, value-mode, and mixed-mode 2D ECharts line series.
• Left line3D rendering unchanged.
• Added backend and UI tests for flag registration, config materialisation, field visibility, store updates, and series options.
• Updated line chart docs and settings docs.
• Regenerated the embedded UI bundle in pkg/template/vizb-ui.gen.go.

Test Result

Testing Steps

• Ran full Go test suite:

go test ./...

• Built/regenerated embedded UI with Node 22:

cd ui
fnm use 22.23.1

corepack pnpm install --frozen-lockfile

EMBED_UI=True corepack pnpm build

• Ran targeted UI tests:

cd ui

fnm use 22.23.1

corepack pnpm test \
  src/components/SettingsPanel.test.ts \
  src/composables/settings/fieldRegistry.test.ts \
  src/composables/useSettingsStore.test.ts \
  src/composables/charts/useLineChartOptions.test.ts

• Smoke-tested --smooth CLI output:

go run . line examples/csv/sales.csv -g region,category -p x,y --smooth -o out.html

• Verified generated HTML contains baked config:

rg -o '"smooth":true' out.html

• Smoke-tested multi-chart override:

go run . examples/csv/sales.csv -g region,category -p x,y -c bar,line --chart line:smooth 

-o dashboard.html

• Verified CLI flag exposure:

go run . line --help | rg smooth
go run . bar --help | rg smooth

expected below script exist for go run . line --help | rg smooth and not for go run . bar --help | rg smooth.

--smooth                 Render smooth curved segments between line chart points

• Manually opened out.html and confirmed: