fix: pre-landing and adversarial review fixes

- landing.css: hardcode --lp-btn to #60a5fa (lesson 104 — no var(--color-*) in landing.css)
- ScriptBuilderInput: suggestion chips now correctly disabled during generation
- ChatSidebar: wrapper onClick no longer fires onSelect while in confirming state
- SessionHistoryPage: fix loadMoreAiSessions race condition with generation counter;
  flow session tab auto-activates when URL params target flow session filters

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/assistant/ChatSidebar.tsx

@@ -189,7 +189,7 @@ function ChatItem({
 
   return (
     <div
-      onClick={onSelect}
+      onClick={confirming ? e => e.stopPropagation() : onSelect}
       className={cn(
         'group flex items-center gap-2 px-3 py-2.5 mx-1.5 rounded-lg cursor-pointer transition-colors',
         confirming