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.

renovate.json

@@ -0,0 +1,29 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": ["config:recommended"],
+  "timezone": "Europe/Paris",
+  "labels": ["bot"],
+  "vulnerabilityAlerts": {
+    "addLabels": ["bug"]
+  },
+  "packageRules": [
+    {
+      "matchManagers": ["pip_requirements"],
+      "matchUpdateTypes": ["patch", "minor"],
+      "automerge": true
+    },
+    {
+      "matchManagers": ["dockerfile"],
+      "matchUpdateTypes": ["patch"],
+      "automerge": true
+    },
+    {
+      "matchUpdateTypes": ["major"],
+      "addLabels": ["major"]
+    },
+    {
+      "matchUpdateTypes": ["minor"],
+      "addLabels": ["minor"]
+    }
+  ]
+}