refactor(web,mobile): drop code left dead by hiding subagent threads

Removing the "Open subagent thread" affordance left the mobile work log
subscribing to item support it no longer reads, and the web sidebar
importing a predicate it no longer calls. Both tripped the lint rule the
CI Check job enforces.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: shivamhwp

apps/mobile/src/features/threads/thread-work-log.tsx

@@ -10,7 +10,6 @@ import { T3_CODE_BRAND_MARK_SOURCE } from "../../components/brandAssets";
 import { cn } from "../../lib/cn";
 import type { ThreadFeedActivity } from "../../lib/threadActivity";
 import Animated, { FadeIn } from "react-native-reanimated";
-import { useV2ItemSupport } from "../../state/v2-item-support";
 import { ThreadActivityInspector } from "./ThreadActivityInspector";
 
 const MAX_VISIBLE_WORK_LOG_ENTRIES = 1;
@@ -112,11 +111,6 @@ function ThreadActivityThreadLink(props: {
   readonly iconColor: import("react-native").ColorValue;
 }) {
   const row = props.activity.projectedItem;
-  const support = useV2ItemSupport({
-    environmentId: props.environmentId,
-    sourceThreadId: row.sourceThreadId,
-    sourceItemId: row.sourceItemId,
-  });
   const navigation = useNavigation();
   const item = row.item;
   let targetThreadId: ThreadId | null = null;

apps/web/src/components/SidebarV2.tsx

@@ -109,7 +109,6 @@ import {
   filterSidebarV2VisibleThreads,
   firstValidTimestampMs,
   hasUnseenCompletion,
-  isSidebarSubagentThread,
   isTrailingDoubleClick,
   orderItemsByPreferredIds,
   resolveAdjacentThreadId,