Add Gitea Actions CI/CD pipeline

Bring nvidia-stock-bot up to the same CI/CD maturity as adguard-cidre:
pytest suite (19 tests), multi-stage Dockerfile with a dedicated test
stage, pinned requests dependency, Gitea Actions workflow (build, smoke
test, unit tests, deprecation check, Trivy critical/high scan, version
bump + registry publish + release), and a Renovate config for automated
dependency updates.

tests/test_notifier.py

@@ -0,0 +1,80 @@
+import importlib
+import sys
+
+VALID_WEBHOOK = "https://discord.com/api/webhooks/123456789012345678/abcdef"
+
+
+def _import_notifier(monkeypatch, test_mode="False", discord_roles=None):
+    monkeypatch.setenv("DISCORD_WEBHOOK_URL", VALID_WEBHOOK)
+    monkeypatch.setenv("PRODUCT_NAMES", "RTX 5090 Founders Edition")
+    monkeypatch.setenv("TEST_MODE", test_mode)
+    if discord_roles is not None:
+        monkeypatch.setenv("DISCORD_ROLES", discord_roles)
+    else:
+        monkeypatch.delenv("DISCORD_ROLES", raising=False)
+    for mod in ("env_config", "notifier"):
+        sys.modules.pop(mod, None)
+    return importlib.import_module("notifier")
+
+
+class FakeResponse:
+    def __init__(self, status_code=204, text=""):
+        self.status_code = status_code
+        self.text = text
+
+
+def test_test_mode_skips_network_call(monkeypatch):
+    notifier = _import_notifier(monkeypatch, test_mode="True")
+    calls = []
+    monkeypatch.setattr(notifier.requests, "post", lambda *a, **k: calls.append((a, k)))
+
+    notifier.send_discord_notification("RTX 5090 Founders Edition", "https://example.com", "1999")
+
+    assert calls == []
+
+
+def test_in_stock_notification_posts_expected_payload(monkeypatch):
+    notifier = _import_notifier(monkeypatch, test_mode="False")
+    captured = {}
+
+    def fake_post(url, json=None, **kwargs):
+        captured["url"] = url
+        captured["json"] = json
+        return FakeResponse()
+
+    monkeypatch.setattr(notifier.requests, "post", fake_post)
+
+    notifier.send_discord_notification("RTX 5090 Founders Edition", "https://example.com/buy", "1999")
+
+    assert captured["url"] == notifier.DISCORD_WEBHOOK_URL
+    assert captured["json"]["content"] == "@everyone"
+    embed = captured["json"]["embeds"][0]
+    assert "RTX 5090 Founders Edition" in embed["title"]
+
+
+def test_out_of_stock_notification_survives_http_error(monkeypatch):
+    notifier = _import_notifier(monkeypatch, test_mode="False")
+    monkeypatch.setattr(notifier.requests, "post", lambda *a, **k: FakeResponse(status_code=500, text="boom"))
+
+    # Should not raise even though the webhook call "fails"
+    notifier.send_out_of_stock_notification("RTX 5090 Founders Edition", "https://example.com", "1999")
+
+
+def test_sku_change_notification_mentions_role_and_skus(monkeypatch):
+    notifier = _import_notifier(monkeypatch, test_mode="False", discord_roles="<@&123456789012345678>")
+    captured = {}
+
+    def fake_post(url, json=None, **kwargs):
+        captured["json"] = json
+        return FakeResponse()
+
+    monkeypatch.setattr(notifier.requests, "post", fake_post)
+
+    notifier.send_sku_change_notification(
+        "RTX 5090 Founders Edition", "old-sku-123", "new-sku-456", "https://example.com"
+    )
+
+    assert "<@&123456789012345678>" in captured["json"]["content"]
+    description = captured["json"]["embeds"][0]["description"]
+    assert "old-sku-123" in description
+    assert "new-sku-456" in description