docs(changelog): add the #1709 fragment

Co-Authored-By: Claude Fable 5.2 <[email protected]>

changelog.d/1709-radio-category-cache.md

@@ -0,0 +1,3 @@
+- Shorten the hitch when the Radio directory loads from about 450 ms to about
+  180 ms. A station's tags and categories are worked out once instead of for
+  every category check (mazy1998, #1709).