ci: configure and stabilize CI/CD pipeline

- fix runner configuration issues
- correct workflow labels and execution environment
- resolve dependency issues in pipeline (python deps)
- improve reliability of automation runs

.gitea/workflows/ci.yml

@@ -0,0 +1,31 @@
+name: ci
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Python syntax check
+        run: |
+          python3 -m py_compile \
+            migration-validation-framework/cli.py \
+            migration-validation-framework/collectors/*.py \
+            migration-validation-framework/validators/*.py \
+            migration-validation-framework/reports/*.py
+
+      - name: Ansible syntax check
+        run: |
+          python3 -m pip install --user ansible
+          ansible-playbook -i enterprise-infra-simulator/inventory/hosts.ini \
+            --syntax-check enterprise-infra-simulator/playbooks/*.yml
+
+      - name: Docker compose validation
+        run: |
+          docker compose -f observability-stack/docker-compose.yml config