test(server): ajoute tests fonctionnels sync et fixtures versionnees (#187)

Fixe .gitignore pour exclure .build-home/ et .pub-cache-local/ des
environnements locaux de build (bruit non versionne). Documente le
checklist d'integration serveur et met a jour le README en consequence.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/test/fixtures/exercises/v1/with_steps.json

@@ -0,0 +1,21 @@
+{
+  "schemaVersion": 2,
+  "id": "exercise-with-steps",
+  "name": "Kettlebell swing",
+  "type": "strength",
+  "steps": [
+    {
+      "id": "step-setup",
+      "order": 0,
+      "title": "Setup",
+      "body": "Hinge with the bell slightly in front of the feet."
+    },
+    {
+      "id": "step-drive",
+      "order": 1,
+      "title": "Drive",
+      "body": "Extend the hips and let the bell float to chest height."
+    }
+  ],
+  "updatedAt": "2026-07-19T10:05:00.000Z"
+}