Top-row chrome: dropdowns layer above the cost number; slight (4px) corners

- Stacking: the actions row is now relative + z-20 — an open settings or
  coverage dropdown paints over the cost number below it (owner report:
  it layered ON TOP of the panel, still hoverable/clickable). The row is
  a stacking context inside the column, so its dropdowns cover the
  number and clicks land on the panel; the number resurfaces untouched
  when the panel closes (verified with elementFromPoint).
- Rectangular look (owner, 2026-09-20): the four top-row controls drop
  rounded-xl (16px theme) to rounded-sm (4px) — gear, coverage, search
  container + input, import container + button; the cost number's hover
  highlight joins the family. Dropdown panels keep their softer cards.

components/graph-coverage.tsx

@@ -102,7 +102,7 @@ export function GraphCoverageControl({ refreshKey = 0 }: { refreshKey?: number }
 				title="Extraction coverage — what the knowledge graph has covered"
 				aria-expanded={open}
 				onClick={() => setOpen((o) => !o)}
-				className={`flex size-9 items-center justify-center rounded-xl border bg-card/85 shadow-lg backdrop-blur transition-colors hover:bg-accent ${
+				className={`flex size-9 items-center justify-center rounded-sm border bg-card/85 shadow-lg backdrop-blur transition-colors hover:bg-accent ${
 					open ? "text-foreground" : "text-muted-foreground hover:text-foreground"
 				}`}
 			>