meta: add dependabot config

[AndersonUece]

Added Dependabot configuration, which automatically checks for dependency updates for npm and GitHub Actions once a week to keep the project compatible with current tools and libraries without manual control.

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Note

Low Risk
Low risk since it only adds Dependabot configuration; any risk is limited to future automated update PRs it will generate.

Overview
Adds .github/dependabot.yml to enable weekly Dependabot update PRs for GitHub Actions and npm dependencies at the repository root.

^{Written by Cursor Bugbot for commit ebc51e0. This will update automatically on new commits. Configure here.}