Fix: milestone routes use milestone_code, config check via backend

- Milestone navigation now uses milestone_code instead of numeric id
- MilestoneDetailPage uses milestone.id (numeric) for project-scoped API calls
- App.tsx checks /config/status on backend first, falls back to wizard
- Added milestone_code to Milestone type
- Fixed MilestoneDetailPage to use fetched milestone.id for sub-queries

src/pages/MilestonesPage.tsx

@@ -49,7 +49,7 @@ export default function MilestonesPage() {
 
       <div className="milestone-grid">
         {milestones.map((ms) => (
-          <div key={ms.id} className="milestone-card" onClick={() => navigate(`/milestones/${ms.id}`)}>
+          <div key={ms.id} className="milestone-card" onClick={() => navigate(`/milestones/${ms.milestone_code || ms.id}`)}>
             <div className="milestone-card-header">
               <span className={`badge status-${ms.status}`}>{ms.status}</span>
               <h3>{ms.title}</h3>