chore(infra): update dependabot.yml to monthly schedule with update-type split [INF-0000] (#35587)

## Summary

- Changes Dependabot schedule from `weekly` to `monthly` across all 4
update entries to reduce PR noise while keeping dependencies current
- Adds `update-types` split (major vs minor+patch) to all dependency
groups so breaking changes arrive in separate PRs from safe updates

## Why

Weekly cadence generates excessive PRs in a monorepo this size. Monthly
is the recommended cadence for non-security version updates (security
updates are handled separately by GitHub). The update-type split ensures
major (breaking) bumps don't get mixed with safe minor/patch updates,
making review easier and safer.

## Test plan

- [x] Verify Dependabot parses the updated config without errors (check
Settings > Code security > Dependabot)
- [x] Confirm next scheduled run produces grouped PRs split by update
type

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Co-authored-by: Claude Opus 4.6 <[email protected]>