fix: restrict spell-check to Deepnote-specific code only

- Remove massive ~1,800 word list from cspell.json
- Add 'files' array to check only src/notebooks/deepnote/, src/kernels/deepnote/, and deepnoteServerNotFoundError.ts
- Update package.json spell-check scripts to use cspell without file globs (respects files config)
- Add minimal 28 technical terms found in Deepnote code (venv, ipykernel, numpy, etc.)
- No longer checks forked Microsoft/vscode-jupyter code

Result: 36 files checked (down from 1,108), 0 spelling issues (down from 15,903)

Author: devin-ai-integration[bot]