clip the canvas wrapper to suppress first-paint overflow

Address Greptile P2 review on PR #4260. Before Chart.js' first
ResizeObserver callback fires the canvas keeps its HTML5 default
size of 300x150. With position: absolute that no longer pushes any
ancestor's intrinsic size, but on a wrapper narrower than 300px the
canvas can still poke past the wrapper for one frame before Chart.js
catches up. Adding overflow: hidden to the relative wrapper clips
that transient overflow and is the pattern Chart.js' own docs
recommend for responsive charts inside flex / grid layouts. No
steady-state behaviour change because the canvas is already sized to
the wrapper once Chart.js takes over; the React tooltip lives
outside this wrapper so it remains visible.

src/components/charts/Chart.tsx

@@ -133,7 +133,7 @@ export function Chart({
           wrapper sizes purely from its parent (width: 100%, height: 100%)
           and Chart.js' ResizeObserver picks up viewport changes.
         */}
-        <div style={{ position: 'relative', width: '100%', height: '100%' }}>
+        <div style={{ position: 'relative', width: '100%', height: '100%', overflow: 'hidden' }}>
           <canvas ref={canvas} style={{ position: 'absolute', top: 0, left: 0 }} />
         </div>
       </Box>