ci: pipeline seed séparé (.woodpecker/seed.yml, event: manual)

Pipeline dédié au seeding DB, déclenché uniquement manuellement.
Retire le step seed du pipeline principal.

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

.woodpecker/seed.yml

@@ -0,0 +1,15 @@
+when:
+  - branch: main
+    event: manual
+
+steps:
+  - name: seed
+    image: docker:27-cli
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock
+      - /opt/libredecision:/opt/libredecision
+    commands:
+      - |
+        PROJECT=$(grep '^COMPOSE_PROJECT_NAME=' /opt/libredecision/.env | cut -d= -f2)
+        echo "Seeding $PROJECT-backend..."
+        docker exec "$PROJECT-backend" python seed.py