refactor: update API key source in .env.example and enhance README with badges and feature descriptions

feat: improve logging levels for HTTP clients and add detailed logging in premium and stars purchase methods
chore: remove unused transaction utility and adjust wallet processing logic
test: add end-to-end integration test for buying Stars

tests/003_test_integration.py

@@ -0,0 +1,13 @@
+"""End-to-end integration test: buy 50 Stars for @bohd4nx.
+
+Requires cookies.json and a valid .env (API_KEY + SEED).
+Auto-skipped when cookies are unavailable (e.g. local runs without secrets).
+"""
+
+from app.methods.stars import buy_stars
+
+
+async def test_buy_stars_e2e(cookies):
+    result = await buy_stars("@bohd4nx", 50)
+    assert result["success"] is True, result.get("error")
+    assert result["data"]["transaction_id"]