Gracefully handle missing config file in watcher

[karlTGA]

Summary

• Continue watching when the config file is removed, logging a warning and skipping cron generation until it returns
• Add regression test simulating config file removal and recreation without Docker or network dependencies
• Start watcher even if the config file is missing at startup and skip initial cron generation with warning
• Simplify test runner to execute all test scenarios
• Merge latest upstream changes with strict bash options

Testing

• bash tests/config_parser_test.sh
• bash tests/watch_config_test.sh
• bash test.sh

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https://chatgpt.com/codex/tasks/task_e_68b42c2b8158832f812b93748b77f615