infra(matrix): CI validation + local integration test for #166/#183

- Add Gitea workflow to validate matrix scaffold on every push/PR (#183)
- Add docker-compose.test.yml for local Conduit testing (#166)
- Add test-local-integration.sh: end-to-end Hermes Matrix adapter
  proof without requiring public DNS/domain

This makes #183 self-enforcing and proves #166 is execution-ready
pending only the host/domain decision in #187.

.gitea/workflows/validate-matrix-scaffold.yml

@@ -0,0 +1,39 @@
+name: Validate Matrix Scaffold
+
+on:
+  push:
+    branches: [main, master]
+    paths:
+      - "infra/matrix/**"
+      - ".gitea/workflows/validate-matrix-scaffold.yml"
+  pull_request:
+    branches: [main, master]
+    paths:
+      - "infra/matrix/**"
+
+jobs:
+  validate-scaffold:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+
+      - name: Install dependencies
+        run: pip install pyyaml
+
+      - name: Validate Matrix/Conduit scaffold
+        run: python3 infra/matrix/scripts/validate-scaffold.py --json
+
+      - name: Check shell scripts are executable
+        run: |
+          test -x infra/matrix/deploy-matrix.sh
+          test -x infra/matrix/host-readiness-check.sh
+          test -x infra/matrix/scripts/deploy-conduit.sh
+
+      - name: Validate docker-compose syntax
+        run: |
+          docker compose -f infra/matrix/docker-compose.yml config > /dev/null