chore(pilot): remove deprecated SuggestedFix task-lane card

Superseded by ProposalBanner (Phase 8). The import was already removed
from AssistantChatPage in the previous commit; this deletes the orphaned
file itself and strips the now-unused suggestedFixSlot prop from
TaskLane's interface and both call sites.

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

frontend/src/components/assistant/TaskLane.tsx

@@ -43,8 +43,6 @@ interface TaskLaneProps {
   // shape lets the parent own fact-fetching and state-version polling without
   // pulling that concern into TaskLane.
   whatWeKnowSlot?: React.ReactNode
-  // Phase 3: Suggested fix card, rendered below Diagnostic Checks.
-  suggestedFixSlot?: React.ReactNode
   // Phase 3: bottom-of-lane slot for the Resolve action bar + preview popover
   // (parent owns state). Renders inside the scrollable body so the popover
   // stays anchored as the lane scrolls.
@@ -79,7 +77,7 @@ export function clearTaskState(sessionId: string) {
 
 // ── Component ──
 
-export function TaskLane({ questions, actions, sessionId, onSubmit, onClose, loading, whatWeKnowSlot, suggestedFixSlot, bottomSlot, variant = 'side' }: TaskLaneProps) {
+export function TaskLane({ questions, actions, sessionId, onSubmit, onClose, loading, whatWeKnowSlot, bottomSlot, variant = 'side' }: TaskLaneProps) {
   const isDrawer = variant === 'drawer'
   const [tasks, setTasks] = useState<TaskResponse[]>(() => {
     // Try to restore saved state for this session (preserves user's in-progress answers)
@@ -535,15 +533,11 @@ export function TaskLane({ questions, actions, sessionId, onSubmit, onClose, loa
           </section>
         )}
 
-        {/* ── Suggested fix (Phase 3) ── */}
-        {suggestedFixSlot}
-
         {/* Quiet-state hint: lane is open (facts exist), but AI hasn't
             proposed a next step yet. Keeps the lane from feeling "finished"
             when the engineer still expects a question / fix to arrive. */}
         {questionTasks.length === 0
           && actionTasks.length === 0
-          && !suggestedFixSlot
           && !loading && (
           <div className="text-[0.6875rem] italic text-muted-foreground px-1 py-2">
             No open questions — send a message or add a note; the AI will follow up.