chart toolbar: inline Image/Video/Report next to Copy/DL, icon-only

[Flotapponnier]

Follow-up to unify the four share/export controls into one visual toolbar next to the chart.

Changes

• Image / Video / Report: dropped the text labels, kept the icons only. Same light border-ink/15 shadow-sm pill style, tighter padding (p-1.5) so they read as compact icon buttons.
• Placement: removed from the top-of-page nav row, moved into each chart's `headerActions` slot via a new `pageActions` prop on `BenchmarkBody`. They now render immediately to the left of the ViewSwitcher, on the same baseline as the chart-owned Copy/Download pill. One toolbar per visible chart, no floating cluster above the page.
• BenchmarkBody merges them into every view's header (ranked bar, timeseries, distribution, donut, countLeaderboard) so the affordance never disappears when the reader switches view.

Test plan

• Any bench page → look at top: no more Image/Video/Report row
• Look at the chart card header → icons appear next to the ViewSwitcher on the right
• Copy/Download pill still sits at the top of the chart header
• Icons remain visible when switching between rankedBar / timeseries / distribution / donut views