Show required specialization labels on course buttons

Replace top-level mutual exclusion banner with dynamic per-course
"Required for ..." labels derived from specialization data. Labels
appear on any course that is a specialization prerequisite, across
all elective sets.

app/src/App.tsx

@@ -5,7 +5,7 @@ import { SpecializationRanking } from './components/SpecializationRanking';
 import { ModeToggle } from './components/ModeToggle';
 import { CourseSelection } from './components/CourseSelection';
 import { CreditLegend } from './components/CreditLegend';
-import { ModeComparison, MutualExclusionWarnings } from './components/Notifications';
+import { ModeComparison } from './components/Notifications';
 import { optimize } from './solver/optimizer';
 
 function App() {
@@ -53,7 +53,6 @@ function App() {
 
       <ModeToggle mode={state.mode} onSetMode={setMode} />
 
-      <MutualExclusionWarnings pinnedCourses={state.pinnedCourses} />
       <ModeComparison
         result={optimizationResult}
         altResult={altResult}

app/src/components/CourseSelection.tsx

@@ -1,8 +1,17 @@
 import { ELECTIVE_SETS } from '../data/electiveSets';
+import { SPECIALIZATIONS } from '../data/specializations';
 import { coursesBySet } from '../data/lookups';
 import type { Term } from '../data/types';
 import type { SetAnalysis } from '../solver/decisionTree';
 
+// Reverse map: courseId → specialization names that require it
+const requiredForSpec: Record<string, string[]> = {};
+for (const spec of SPECIALIZATIONS) {
+  if (spec.requiredCourseId) {
+    (requiredForSpec[spec.requiredCourseId] ??= []).push(spec.name);
+  }
+}
+
 interface CourseSelectionProps {
   pinnedCourses: Record<string, string | null>;
   treeResults: SetAnalysis[];
@@ -79,30 +88,37 @@ function ElectiveSet({
         <div style={{ display: 'flex', flexDirection: 'column', gap: '4px' }}>
           {courses.map((course) => {
             const ceiling = ceilingMap.get(course.id);
+            const reqFor = requiredForSpec[course.id];
             return (
               <button
                 key={course.id}
                 onClick={() => onPin(course.id)}
                 style={{
-                  display: 'flex', justifyContent: 'space-between', alignItems: 'center',
+                  display: 'flex', flexDirection: 'column', alignItems: 'stretch',
                   textAlign: 'left', padding: '6px 10px',
                   border: '1px solid #e5e7eb', borderRadius: '4px',
                   background: '#fff', cursor: 'pointer', fontSize: '13px', color: '#333',
-                  gap: '8px',
                 }}
               >
-                <span style={{ flex: 1 }}>{course.name}</span>
-                {ceiling && (
-                  <span style={{
-                    fontSize: '11px', whiteSpace: 'nowrap', fontWeight: 600,
-                    color: ceiling.ceilingCount >= 3 ? '#16a34a' : ceiling.ceilingCount >= 2 ? '#2563eb' : '#666',
-                  }}>
-                    {ceiling.ceilingCount} spec{ceiling.ceilingCount !== 1 ? 's' : ''}
-                    {ceiling.ceilingSpecs.length > 0 && (
-                      <span style={{ fontWeight: 400, color: '#888', marginLeft: '3px' }}>
-                        ({ceiling.ceilingSpecs.join(', ')})
-                      </span>
-                    )}
+                <div style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center', gap: '8px' }}>
+                  <span style={{ flex: 1 }}>{course.name}</span>
+                  {ceiling && (
+                    <span style={{
+                      fontSize: '11px', whiteSpace: 'nowrap', fontWeight: 600,
+                      color: ceiling.ceilingCount >= 3 ? '#16a34a' : ceiling.ceilingCount >= 2 ? '#2563eb' : '#666',
+                    }}>
+                      {ceiling.ceilingCount} spec{ceiling.ceilingCount !== 1 ? 's' : ''}
+                      {ceiling.ceilingSpecs.length > 0 && (
+                        <span style={{ fontWeight: 400, color: '#888', marginLeft: '3px' }}>
+                          ({ceiling.ceilingSpecs.join(', ')})
+                        </span>
+                      )}
+                    </span>
+                  )}
+                </div>
+                {reqFor && (
+                  <span style={{ fontSize: '11px', color: '#92400e', marginTop: '2px' }}>
+                    Required for {reqFor.join(', ')}
                   </span>
                 )}
               </button>

app/src/components/Notifications.tsx

@@ -33,33 +33,3 @@ export function ModeComparison({
   );
 }
 
-export function MutualExclusionWarnings({ pinnedCourses }: { pinnedCourses: Record<string, string | null> }) {
-  const warnings: string[] = [];
-  const spr4Pin = pinnedCourses['spr4'];
-
-  if (!spr4Pin) {
-    warnings.push('Spring Set 4: choosing Sustainability for Competitive Advantage eliminates Entrepreneurship & Innovation (and vice versa).');
-  } else if (spr4Pin === 'spr4-sustainability') {
-    warnings.push('Entrepreneurship & Innovation is permanently unavailable (required course is in Spring Set 4, pinned to Sustainability).');
-  } else if (spr4Pin === 'spr4-foundations-entrepreneurship') {
-    warnings.push('Sustainable Business & Innovation is permanently unavailable (required course is in Spring Set 4, pinned to Foundations of Entrepreneurship).');
-  }
-
-  if (warnings.length === 0) return null;
-
-  return (
-    <div style={{ marginBottom: '8px' }}>
-      {warnings.map((w, i) => (
-        <div
-          key={i}
-          style={{
-            background: '#fef3c7', border: '1px solid #fcd34d', borderRadius: '6px',
-            padding: '8px 10px', fontSize: '12px', color: '#92400e', marginBottom: '4px',
-          }}
-        >
-          {w}
-        </div>
-      ))}
-    </div>
-  );
-}