remove depbot (#4122)

<!-- CURSOR_SUMMARY -->
> [!NOTE]
> **Low Risk**
> Configuration-only removal with no application or runtime code
changes; dependency updates will need to be handled manually unless
replaced elsewhere.
> 
> **Overview**
> **Removes automated dependency update configuration** by deleting
`.github/dependabot.yml`, so Dependabot will no longer open weekly PRs
for npm (root workspace, templates, examples), Cargo, or pip
dependencies with the previous grouping, labels, and `@types/node`
ignore rules.
> 
> No other files in this diff change CI or release behavior; any
remaining `dependabot[bot]` checks in workflows are unchanged.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
ca2f18c. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: georgevanderson