chore(renovate): add shared preset config

[cpritchett]

Renovate onboarding — shared preset

This PR configures Renovate to use the Blavity shared preset.

Previous config status: No Renovate config
Detected stacks: node, python

What this config does

• Extends github>blavity/renovate-config for org-wide defaults (schedules, automerge rules, grouping, merge confidence badges, OSV vulnerability alerts)
• Adds stack-specific packageRules grouping where applicable

What the shared preset provides

• Business-hours schedule (6am–4pm ET weekdays)
• Patch/minor automerge after CI; major requires review
• Security vulnerability alerts (immediate, bypass schedule)
• Merge confidence badges on all PRs
• Lock file maintenance on Saturday mornings
• GitHub Actions digest pinning

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Opened by onboard.js

[Copilot]

Pull request overview

Adds initial Renovate configuration for the repository by onboarding the Blavity shared preset, enabling standardized dependency update automation aligned with org-wide defaults.

Changes:

• Introduces renovate.json5 extending github>blavity/renovate-config.
• Adds a packageRules grouping for Python dependency managers (if/when present in the repo).

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