fix(flowpilot): fix message bar hidden behind fixed action bar

The message bar was in normal document flow but the action bar uses
position:fixed at bottom:0, covering it. Now the message bar is also
fixed-positioned at bottom:60px (above the action bar), matching the
same left offset pattern. Added extra bottom padding to the
conversation column for clearance.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/flowpilot/FlowPilotSession.tsx

@@ -194,8 +194,8 @@ export function FlowPilotSession({
 
       {/* Main content area: conversation + sidebar */}
       <div className="flex flex-1 min-h-0">
-        {/* Conversation column — pb-20 provides clearance for the fixed action bar */}
-        <div ref={scrollRef} className="flex-1 overflow-y-auto p-3 pb-20 sm:p-4 sm:pb-20 lg:p-6 lg:pb-20">
+        {/* Conversation column — pb-32 provides clearance for the fixed message bar + action bar */}
+        <div ref={scrollRef} className="flex-1 overflow-y-auto p-3 pb-32 sm:p-4 sm:pb-32 lg:p-6 lg:pb-32">
           <div className="mx-auto max-w-2xl space-y-3">
             {allSteps.map((step) => (
               <FlowPilotStepCard