Fixes two critical issues preventing Traefik proxy startup:
1. TypeError when restarting proxy: Handle null return from get_traefik_versions()
- Add null check before dispatching CheckTraefikVersionForServerJob
- Log warning when version data is unavailable
- Prevents: "Argument #2 must be of type array, null given"
2. Docker network error: Filter out predefined Docker networks
- Add isDockerPredefinedNetwork() helper to centralize network filtering
- Apply filtering in collectDockerNetworksByServer() before operations
- Apply filtering in generateDefaultProxyConfiguration()
- Prevents: "operation is not permitted on predefined default network"
Also: Move $cachedVersionsFile assignment after null check in Proxy.php
Tests: Added 7 new unit tests for network filtering function
All existing tests pass with no regressions
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Co-Authored-By: Claude <noreply@anthropic.com>
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