feat: Canvas pie chart — add "Other" grouping + hover percentages

[ericokuma]

Summary

Pie/donut charts with many slices are now readable via smart "Other" grouping, and hovering any slice shows percentage of total.

What changed

Smart "Other" Grouping (other-grouping.ts)

• Dynamic algorithm: walks largest slices first, stops when remaining ≤20% of total (hard cap of 10 visible slices)
• When only 0–1 items would be grouped, "Other" is skipped entirely
• showOther YAML config (default true) controls grouping
• Existing limit on the color field bypasses dynamic algorithm for a fixed cutoff

"Other" Slice Appearance

• Muted color: light #d1d5db / dark #4b5563
• Applied in both Vega-Lite spec color scale and canvas color mapping
• "Other" appears last in legend with the muted color

Hover Tooltips with Percentages (pie-tooltip.ts)

• Named slices: shows name, formatted value, and percentage (1 decimal)
• "Other" slice: mini-leaderboard tooltip with top 5 grouped items (value + %), plus "and N more" footer
• Percentages calculated against true grand total (fetched via separate aggregation query)

Data Pipeline

• Added optional dataTransformer to ChartDataDependencies for pre-chart data transformation
• CircularChartProvider.transformData() applies "Other" grouping before data reaches Vega-Lite
• Total query now fires whenever showOther is enabled (not just showTotal)
• API query limit is at least DEFAULT_COLOR_LIMIT even when user sets a low explicit limit

Files changed

File	Change
circular/other-grouping.ts	New — grouping algorithm + tooltip data helpers
circular/other-grouping.spec.ts	New — 13 unit tests covering all acceptance criteria
circular/pie-tooltip.ts	New — custom Vega tooltip formatter for pie/donut
circular/pie.ts	Percentage transform, "Other" color in Vega spec
circular/CircularChartProvider.ts	showOther on spec, data transform, total query logic
Chart.svelte	"Other" color mapping, pie tooltip formatter wiring
data-provider.ts	Optional dataTransformer in data pipeline
BaseChart.ts	getDataTransformer() / getOtherGroupResult() methods
CircularChart.ts	Override transformer + other-group-result methods
CanvasChart.svelte	Pass otherGroupResult to Chart
selector.ts	Wire dataTransformer into getChartDataForCanvas

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!

Linear Issue: APP-818