Colab Tutorial re-link

[janezdu]

Contributor: Jane Du (zd16@illinois.edu)

Contribution Type: Documentation / Tutorials

Description:
Basically unbreaking the tutorial links with new ownership of Colab Notebooks on Google Drive.

• Upload tutorials 0-7 colabs to gdrive, including the 2 previously unbroken ones (1.pyhealth.datasets, 2.pyhealth.tasks`)
• Refreshes stale Colab URLs across the docs (Tutorial 1 datasets, Tutorial 2 tasks, Tutorial 6 tokenizer), and makes
• Restores Tutorial 6 (pyhealth.tokenizer) which was lost in the UIUC Google Drive purge
• adds !pip install pyhealth cells to all tutorials
• external links in the docs open in a new tab

Files to Review:

• examples/tutorials/tutorial_pyhealth_tokenizer.ipynb — new tutorial notebook
• examples/tutorials/orig_tutorial_pyhealth_{tasks,datasets}.ipynb — renamed backups (_orig suffix → orig_ prefix)
• examples/tutorials/tutorial_pyhealth_*.ipynb — added install cells + retitled duplicate "Summary" in the data tutorial
• docs/tutorials.rst, README.rst, docs/api/{tasks,datasets}.rst — refreshed Colab IDs
• docs/conf.py, docs/_static/external_links.js — open-external-links-in-new-tab
• chat-assistant/corpus/*.txt — same URL refresh propagated through the chatbot corpus
• examples/tutorial_stagenet_comprehensive.ipynb — fixed inline Colab cross-references (incl. a pre-existing typo)

[jhnwu3]

Thank you!!!