chore: add Renovate config (python-uv preset) (#472)

## Summary
- Adds `renovate.json` extending the shared `python-uv` preset from
`Unstructured-IO/renovate-config`
- Enables automated dependency update PRs for Python
(pep621/pyproject.toml), Dockerfiles, and GitHub Actions
- Non-major updates are grouped; major updates get individual PRs
- Vulnerability alerts are prioritized and unscheduled
- Schedule: weekly on Monday mornings (ET)

## Test plan
- [ ] Verify Renovate bot picks up the config and creates dependency
update PRs
- [ ] Confirm PR grouping behavior matches expectations

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

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Only adds Renovate configuration; no runtime code paths change, with
the main impact being automated dependency update PR generation.
> 
> **Overview**
> Adds `renovate.json` configured to extend the shared
`github>Unstructured-IO/renovate-config:python-uv` preset, enabling
Renovate-driven automated dependency update PRs for this repo.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
8492ed1. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: lawrence-u10d

renovate.json

@@ -0,0 +1,4 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": ["github>Unstructured-IO/renovate-config:python-uv"]
+}