feat(slice-4): VERSION file + versioned /healthz — the flotilla verify contract (§8.1)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/tests/test_healthz.py

@@ -1,14 +1,20 @@
+from pathlib import Path
+
 from fastapi.testclient import TestClient
 
 from app.main import create_app
 
+# /healthz reports the VERSION file's value — the flotilla deploy gate compares
+# body.version against the pinned target (flotilla-core SPEC §8.1 phase 8).
+_VERSION = (Path(__file__).resolve().parents[2] / "VERSION").read_text().strip()
+
 
 def test_healthz_ok_on_migrated_empty_db(fresh_db_url):
     app = create_app(database_url=fresh_db_url)
     with TestClient(app) as client:
         resp = client.get("/healthz")
     assert resp.status_code == 200
-    assert resp.json() == {"status": "ok"}
+    assert resp.json() == {"status": "ok", "version": _VERSION}
 
 
 def test_startup_migrates_from_empty(fresh_db_url):