Fix default namespace lookup, bump dependencies

[austin-denoble]

Problem

Default namespace representation shifted in describe_index_stats for 2025-10. We need to check for both possibilities in the sample app.

There were also a number of NPM high severity vulnerabilities that needed to be bumped:

• vitest
• @vitest/coverage
• nodemon

Solution

• Check for either "" or "__default__" when looking up namespaces.
• Run npm audit to fix high severity vulnerabilities: vitest, @vitest/coverage-v8, and nodemon.
  • Bumped to more recent version of node for this (v20).

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Infrastructure change (CI configs, etc)
• Non-code change (docs, etc)
• None of the above: (explain here)

Test Plan

CI - testing coverage