Let quarto know about bundled ipykernel

[testlabauto]

System details:

Positron and OS details:

Positron Version: 2025.06.0 (Universal) build 124 Code - OSS Version: 1.100.0 Commit: 383e237a5cdd8bc770de7aaa275267eeb984ad95 Date: 2025-05-22T03:33:38.449Z Electron: 34.5.1 Chromium: 132.0.6834.210 Node.js: 20.19.0 V8: 13.2.152.41-electron.0 OS: Darwin arm64 24.5.0

Interpreter details:

All python

Describe the issue:

Currently to run a preview of a quarto file in Positron, one needs to have ipykernel installed in their environment. This doesn't seem sensible for users since ipykernel is bundled in Positron. We should make the bundled ipykernel "known" to the terminal so that this no longer necessary.

Steps to reproduce the issue:

1. Preview a python qmd with a python env that doesn't have ipykernel installed
2. Hit confusing error about not being able to find python3

Expected or desired behavior:

Can preview python qmd without installing ipykernel

Were there any error messages in the UI, Output panel, or Developer Tools console?

No