feat: add ranking table sync and API endpoints

Sync Ranking table from SQL Server to PostgreSQL with ranking_ca,
ranking_qte, ranking_mag_* metrics. Expose via /api/ranking and
integrate into /api/articles/:id/referentiel response.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app.js

@@ -10,6 +10,7 @@ const stockRouter       = require('./routes/stock');
 const mouvementsRouter  = require('./routes/mouvements');
 const performanceRouter = require('./routes/performance');
 const syncRouter        = require('./routes/sync');
+const rankingRouter     = require('./routes/ranking');
 
 const app = express();
 app.use(express.json());
@@ -34,6 +35,7 @@ app.use('/api/stock',        stockRouter);
 app.use('/api/mouvements',   mouvementsRouter);
 app.use('/api/performance',  performanceRouter);
 app.use('/api/sync',         syncRouter);
+app.use('/api/ranking',      rankingRouter);
 
 // 404
 app.use((req, res) => {