polish(channel): tighten toolbar-to-grid gap + restore top scroll fade

Two UAT nits on the channel page:
- the chip-row-to-cards gap was ~36px (toolbar pb-3 + wrapper pb-2 + grid
  pt-3 stacking); drop the wrapper/grid pads so the toolbar's own pb-3 is
  the only gap (~15px).
- restore the page scroller's TOP edge fade. It was dropped when the chrome
  was a sticky sub-header (the fade bit into it); now the chrome is a fixed
  band ABOVE the scroller, so the top fade correctly hints at cards
  scrolling up under the toolbar. Reverts the useScrollFade edges option.

Suite 15/15, tsc + knip clean.

frontend/src/lib/useScrollFade.ts

@@ -7,17 +7,10 @@ import { useEffect, useState, type CSSProperties } from "react";
 // to attach to the scroller and the mask `style` to spread onto it. Uses a node-state callback
 // ref (not useRef) so the effect (re)runs whenever the element attaches — e.g. a SidePanel that
 // mounts collapsed and only renders its scroll body once expanded still wires up correctly.
-// `edges` gates which ends fade. The page scroller passes `{ top: false }`: its top is delimited by
-// the fixed/sticky module chrome (header, toolbar band, a sticky sub-header), so a top fade there
-// would only bite into that chrome instead of hinting at more content.
-export function useScrollFade(
-  fadePx = 20,
-  edges: { top?: boolean; bottom?: boolean } = {},
-): {
+export function useScrollFade(fadePx = 20): {
   ref: (node: HTMLElement | null) => void;
   style: CSSProperties;
 } {
-  const { top: fadeTop = true, bottom: fadeBottom = true } = edges;
   const [el, setEl] = useState<HTMLElement | null>(null);
   const [fade, setFade] = useState({ up: false, down: false });
 
@@ -60,8 +53,8 @@ export function useScrollFade(
     };
   }, [el]);
 
-  const topPx = fadeTop && fade.up ? fadePx : 0;
-  const bottomPx = fadeBottom && fade.down ? fadePx : 0;
-  const mask = `linear-gradient(to bottom, transparent, #000 ${topPx}px, #000 calc(100% - ${bottomPx}px), transparent)`;
+  const mask = `linear-gradient(to bottom, transparent, #000 ${fade.up ? fadePx : 0}px, #000 calc(100% - ${
+    fade.down ? fadePx : 0
+  }px), transparent)`;
   return { ref: setEl, style: { maskImage: mask, WebkitMaskImage: mask } };
 }