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/full_combo.json

@@ -0,0 +1,51 @@
+{
+  "schemaVersion": 5,
+  "id": "exercise-full-combo",
+  "name": "Intervals complex",
+  "type": "mixed",
+  "category": "full_body",
+  "media": {
+    "coverAssetId": "media-cover-1",
+    "videoAssetId": "media-video-1"
+  },
+  "steps": [
+    {
+      "id": "step-row",
+      "order": 0,
+      "title": "Row",
+      "body": "Complete calories before moving on.",
+      "defaultDurationSeconds": 60
+    },
+    {
+      "id": "step-thruster",
+      "order": 1,
+      "title": "Thruster",
+      "body": "Break sets only if form degrades.",
+      "defaultReps": 15
+    }
+  ],
+  "score": {
+    "mode": "for_time",
+    "unit": "seconds",
+    "capSeconds": 900
+  },
+  "chrono": {
+    "mode": "elapsed",
+    "autoStart": true
+  },
+  "timers": {
+    "preparationSeconds": 20,
+    "workSeconds": 180,
+    "restSeconds": 60
+  },
+  "chainOverrides": {
+    "nextExerciseId": "exercise-cooldown",
+    "inheritRest": false
+  },
+  "legacy": {
+    "unknownClientField": {
+      "nested": ["preserve", 1, true, null]
+    }
+  },
+  "updatedAt": "2026-07-19T10:20:00.000Z"
+}