fix(pilot): drop sticky section headers in task lane

Each lane section (What we know, Questions, Diagnostic Checks, Suggested
fix) had its own `position: sticky; top: 0` header. As the engineer
scrolled past a section, that section's header would pin until the
section's bottom edge cleared the viewport, producing an "orphaned"
label floating over unrelated content below. Headers now scroll with
their content — in a 340px-wide lane the affordance was negative value.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/assistant/TaskLane.tsx

@@ -311,7 +311,7 @@ export function TaskLane({ questions, actions, sessionId, onSubmit, onClose, loa
         {/* ── Questions Section ── */}
         {questionTasks.length > 0 && (
           <section>
-            <div className="sticky top-0 z-10 pb-2" style={{ background: 'var(--color-bg-page)' }}>
+            <div className="pb-2">
               <div className="flex items-center gap-2 text-[10px] font-semibold uppercase tracking-[1.2px] text-muted-foreground pl-0.5">
                 <span className="w-1.5 h-1.5 rounded-full bg-accent" />
                 Questions
@@ -406,7 +406,7 @@ export function TaskLane({ questions, actions, sessionId, onSubmit, onClose, loa
         {/* ── Checks Section ── */}
         {actionTasks.length > 0 && (
           <section>
-            <div className="sticky top-0 z-10 pb-2" style={{ background: 'var(--color-bg-page)' }}>
+            <div className="pb-2">
               <div className="flex items-center gap-2 text-[10px] font-semibold uppercase tracking-[1.2px] text-muted-foreground pl-0.5">
                 <span className="w-1.5 h-1.5 rounded-full bg-accent" />
                 Diagnostic Checks

frontend/src/components/pilot/sections/SuggestedFix.tsx

@@ -43,7 +43,7 @@ export function SuggestedFix({ fix, onDismiss, onActivate, panelOpen }: Suggeste
 
   return (
     <section>
-      <div className="sticky top-0 z-10 pb-2" style={{ background: 'var(--color-bg-page)' }}>
+      <div className="pb-2">
         <div className="flex items-center gap-2 text-[10px] font-semibold uppercase tracking-[1.2px] text-muted-foreground pl-0.5">
           <span className="w-1.5 h-1.5 rounded-full bg-warning" />
           Suggested fix

frontend/src/components/pilot/sections/WhatWeKnow.tsx

@@ -43,7 +43,7 @@ export function WhatWeKnow({
         'bg-gradient-to-b from-success/[0.05] to-transparent',
       )}
     >
-      <div className="sticky top-0 z-10 pb-2" style={{ background: 'var(--color-bg-page)' }}>
+      <div className="pb-2">
         <div className="flex items-center gap-2 text-[10px] font-semibold uppercase tracking-[1.2px] text-muted-foreground pl-0.5">
           <span className="w-1.5 h-1.5 rounded-full bg-success" />
           What we know