feat: move feature action buttons to pending column header

Move the "Add Feature" (+) and "Expand Project" (sparkles) buttons from
the top navigation bar to the Pending column header in the Kanban board.

Changes:
- KanbanColumn: Add optional onAddFeature, onExpandProject, and
  showExpandButton props; render action buttons in column header
- KanbanBoard: Accept and pass action handlers to the Pending column
- App: Remove buttons from header, pass handlers to KanbanBoard

This improves UX by placing feature creation actions contextually near
the pending features they affect. Keyboard shortcuts (N, E) still work.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ui/src/components/KanbanColumn.tsx

@@ -1,4 +1,5 @@
 import { FeatureCard } from './FeatureCard'
+import { Plus, Sparkles } from 'lucide-react'
 import type { Feature } from '../lib/types'
 
 interface KanbanColumnProps {
@@ -7,6 +8,9 @@ interface KanbanColumnProps {
   features: Feature[]
   color: 'pending' | 'progress' | 'done'
   onFeatureClick: (feature: Feature) => void
+  onAddFeature?: () => void
+  onExpandProject?: () => void
+  showExpandButton?: boolean
 }
 
 const colorMap = {
@@ -21,6 +25,9 @@ export function KanbanColumn({
   features,
   color,
   onFeatureClick,
+  onAddFeature,
+  onExpandProject,
+  showExpandButton,
 }: KanbanColumnProps) {
   return (
     <div
@@ -32,10 +39,34 @@ export function KanbanColumn({
         className="px-4 py-3 border-b-3 border-[var(--color-neo-border)]"
         style={{ backgroundColor: colorMap[color] }}
       >
-        <h2 className="font-display text-lg font-bold uppercase flex items-center justify-between text-[var(--color-neo-text)]">
-          {title}
-          <span className="neo-badge bg-white text-[var(--color-neo-text)]">{count}</span>
-        </h2>
+        <div className="flex items-center justify-between">
+          <h2 className="font-display text-lg font-bold uppercase flex items-center gap-2 text-[var(--color-neo-text)]">
+            {title}
+            <span className="neo-badge bg-white text-[var(--color-neo-text)]">{count}</span>
+          </h2>
+          {(onAddFeature || onExpandProject) && (
+            <div className="flex items-center gap-2">
+              {onAddFeature && (
+                <button
+                  onClick={onAddFeature}
+                  className="neo-btn neo-btn-primary text-sm py-1.5 px-2"
+                  title="Add new feature (N)"
+                >
+                  <Plus size={16} />
+                </button>
+              )}
+              {onExpandProject && showExpandButton && (
+                <button
+                  onClick={onExpandProject}
+                  className="neo-btn bg-[var(--color-neo-progress)] text-black text-sm py-1.5 px-2"
+                  title="Expand project with AI (E)"
+                >
+                  <Sparkles size={16} />
+                </button>
+              )}
+            </div>
+          )}
+        </div>
       </div>
 
       {/* Cards */}