Add chart views over a collection

## Goal

Simple chart views over the active collection: count, sum, or average of one field grouped by another. Bar and pie are the v0 shapes.

## Scope

* New layout, chart, alongside the others.
* v0 chart shapes: bar, pie.
* v0 aggregations: count, sum, average.
* Group by a select, multiselect, status, date (binned), or checkbox field.
* Configurable axis labels and colors that pick up select option colors where they exist.

## Out of scope

* Multi-chart dashboards or pages.
* Time-series with trend lines.
* Stacked or grouped bars beyond a single dimension.
* Saved chart configs reusable across blocks; each block owns its own.

## Acceptance criteria

* You can pick "chart" as a layout, choose a shape, an aggregation, and a group-by field.
* The chart renders the right values from the current collection.
* Changes to underlying rows update the chart on the next fetch.
* Select option colors carry through to chart series.

Start by reading the existing layout implementations and the entry point that fetches and renders the active collection. Add the chart layout with bar and pie shapes, count/sum/average aggregation, supported group-by fields, configurable labels and colors, then verify the acceptance criteria including updates after the next fetch.

Written by the indexing model from the issue text.