perf(desktop): hoist non-DM channel-name filter into ChannelNavigation provider

Finding [L4] MessageRow channelNames (Tier 3): every row ran
`channels.filter(non-dm).map(name)` in its own useMemo, so the identical
derivation was recomputed once per mounted row and re-ran whenever the channel
list changed. Compute it once in `ChannelNavigationProvider` as
`nonDmChannelNames` (memoised on `[channels]`) and have rows read it directly.

Additive to the context value — `channels` is unchanged, so other consumers are
unaffected.

Co-authored-by: Tyler Longwell <tlongwell@block.xyz>
Signed-off-by: Tyler Longwell <tlongwell@block.xyz>

desktop/src/features/messages/ui/MessageRow.tsx

@@ -198,11 +198,7 @@ export const MessageRow = React.memo(
     );
     const bodyOffsetClass = emojiOnly ? "mt-1" : "-mt-0.5";
 
-    const { channels } = useChannelNavigation();
-    const channelNames = React.useMemo(
-      () => channels.filter((c) => c.channelType !== "dm").map((c) => c.name),
-      [channels],
-    );
+    const { nonDmChannelNames: channelNames } = useChannelNavigation();
 
     const indentRem = getThreadReplyIndentRem(message.depth);
     const descendantGuideOffsetRem = connectDescendants

desktop/src/shared/context/ChannelNavigationContext.tsx

@@ -4,11 +4,15 @@ import type { Channel } from "@/shared/api/types";
 
 type ChannelNavigationContextValue = {
   channels: Channel[];
+  /** Names of non-DM channels, memoised once so render-hot consumers (message
+   *  rows) don't each re-filter the full channel list on every render. */
+  nonDmChannelNames: string[];
 };
 
 const ChannelNavigationContext =
   React.createContext<ChannelNavigationContextValue>({
     channels: [],
+    nonDmChannelNames: [],
   });
 
 export function ChannelNavigationProvider({
@@ -18,7 +22,15 @@ export function ChannelNavigationProvider({
   channels: Channel[];
   children: React.ReactNode;
 }) {
-  const value = React.useMemo(() => ({ channels }), [channels]);
+  const value = React.useMemo(
+    () => ({
+      channels,
+      nonDmChannelNames: channels
+        .filter((c) => c.channelType !== "dm")
+        .map((c) => c.name),
+    }),
+    [channels],
+  );
 
   return (
     <ChannelNavigationContext.Provider value={value}>