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/README.md

@@ -0,0 +1,22 @@
+# Versioned sync fixtures
+
+These JSON files are server contract fixtures. They intentionally model client
+payloads as opaque snapshots: server sync tests must push them, pull them back
+and compare the payloads strictly without teaching the server the client schema.
+
+Structure:
+
+- `exercises/v1/`: first captured exercise fixture batch.
+- `exercises/v2/`: second captured exercise fixture batch used to prove tests
+  can run multiple fixture generations side by side.
+- `programs/v1/`, `workout_templates/v1/`, `workout_histories/v1/`: reusable
+  minimal sync batches for non-exercise resources.
+
+Folder names such as `v1` and `v2` identify fixture batches, not the payload
+schema itself. The authoritative client schema value remains the JSON
+`schemaVersion` field inside each fixture, and tests assert that the server
+preserves that value exactly.
+
+When the client schema changes, add a new fixture batch folder instead of
+rewriting older fixtures. Old fixture versions are kept to verify backward and
+forward compatibility.