chore: standardize renovate.json config

[tim-thacker-nullify]

Summary

• Standardize renovate.json to use config:recommended instead of config:base
• Add standard packageRules: disable major gomod/docker updates, allow major GitHub Actions, disable Python version/pyenv updates, group non-major deps
• Add rebaseWhen: conflicted and consistent schedule * * 1 * *
• Preserved repo-specific separateMajorMinor: false

Test plan

• Verify Renovate picks up the new config on next scheduled run

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