Fix IPAM None handling and add failure log summary to CI

Handle Docker networks where IPAM key exists but has None value by
using `or {}` instead of relying on `.get()` default parameter.

Add CI step to generate SUMMARY.txt from failure logs before uploading
artifacts.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Author: Nils Bars

.github/workflows/ci.yml

@@ -148,6 +148,14 @@ jobs:
           path: tests/coverage_reports/
           retention-days: 7
 
+      - name: Generate failure log summary
+        if: failure()
+        working-directory: tests
+        run: |
+          if [ -d "failure_logs" ]; then
+            uv run python summarize_logs.py || true
+          fi
+
       - name: Upload failure logs
         uses: actions/upload-artifact@v4
         if: failure()

webapp/ref/core/docker.py

@@ -407,7 +407,7 @@ def _get_used_subnets(self) -> set[ipaddress.IPv4Network]:
         used = set()
         for network in self.client.networks.list():
             try:
-                ipam_config = network.attrs.get("IPAM", {}).get("Config") or []
+                ipam_config = (network.attrs.get("IPAM") or {}).get("Config") or []
                 for config in ipam_config:
                     subnet_str = config.get("Subnet")
                     if subnet_str: