Add Databricks notebook installer for Genie Workbench

[hiydavid]

Summary

• Add a Databricks notebook install path in notebooks/install.py that uses notebook-native auth and a shared deployment library.
• Generate deployment source in a workspace folder, patch app.yaml there, and keep the checked-in repo source unchanged.
• Add shared deploy helpers for app setup, workspace source generation, UC/Lakebase/GSO provisioning, Genie Space grants, and verification.
• Update docs and README to treat the notebook installer as the primary path and link detailed behavior to /docs/.
• Fix related installer issues, including app service principal resolution, workspace path normalization, scope handling, and notebook status output.

Testing

• Added and updated unit tests for deploy-lib behavior, source filtering, app.yaml rendering, and app service principal lookup.
• Updated scanner tests to avoid nondeterministic mock behavior.
• Ran targeted Python compilation checks on the notebook installer and new deploy modules.
• Not run: full Databricks integration regression in a live workspace was left to the ongoing notebook testing loop.