[css-color-hdr][editorial] Add JzCzhz prim-sec diagram to the JzCzhz section

Inserts the rec2020-in-JzCzhz diagram (added in a prior commit) as a
figure just before the jzczhz() relative-color paragraph.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: svgeesus

css-color-hdr-1/Overview.bs

@@ -1065,6 +1065,17 @@ Mixing Dynamic Range Limits: the ''dynamic-range-limit-mix()'' function {#dynami
 			</pre>
 		</div>
 
+		<figure id="fig-rec2020-jzczhz">
+			<img src="images/2020-prim-sec-JzCzHz.svg" width=700 height=769
+			alt="diagram of rec2020 primaries and secondaries in JzCzhz">
+			<figcaption>Visualization of the rec2020 color space in JzCzhz.
+				The primaries and secondaries are shown
+				(but in sRGB, not in the correct colors).
+				For comparison, the sRGB primaries and secondaries
+				are also shown, as dashed circles.
+			</figcaption>
+		</figure>
+
 		Within a [=relative color=] syntax ''jzczhz()'' function,
 		the allowed [=component keywords=] are: