fix: mount sessionsRouter at /api/sessions (was /api — causait 404 sur toutes les routes sessions)

backend/src/index.ts

@@ -36,13 +36,13 @@ app.get('/api/health', (_req, res) => {
   res.json({ status: 'ok', service: 'shoottracker', ts: new Date().toISOString() })
 })
 
-app.use('/api/auth',    authRouter)
-app.use('/api/weapons', weaponsRouter)
-app.use('/api',         sessionsRouter)
-app.use('/api',         seriesRouter)
-app.use('/api',         miscRouter)
-app.use('/api',         analyzeRouter)
-app.use('/api/export',  exportRouter)
+app.use('/api/auth',     authRouter)
+app.use('/api/weapons',  weaponsRouter)
+app.use('/api/sessions', sessionsRouter)
+app.use('/api',          seriesRouter)
+app.use('/api',          miscRouter)
+app.use('/api',          analyzeRouter)
+app.use('/api/export',   exportRouter)
 
 // ─── Serve Frontend (production) ─────────────────────────────────────────────
 const publicDir = path.join(__dirname, '..', 'public')