[WIP] VPEX: one-click Databricks Connect environment setup

[rugpanov]

⚠️ WIP / DO-NOT-MERGE — demo / proof-of-concept. Not ready to merge. See the caveat at the bottom.

Summary

Adds a guided one-click "VPEX" flow to set up a Databricks Connect Python environment matched to the selected compute target, with real UI feedback, and auto-adopt the resulting .venv.

It runs the real CLI in the open project folder:

databricks dbconnect init --serverless v4 --profile <detected>
databricks dbconnect sync  --serverless v4 --profile <detected>

parses the CLI's === Phase N: <name> === output to narrate each step, then selects .venv/bin/python automatically.

What's included

• VpexEnvironmentSetup — pre-flight confirmation, phase-aware progress notification, dedicated "VPEX Demo" output channel, and success/failure pop-ups. The run is cancellable (SIGTERM → SIGKILL).
• Auto-adopt interpreter — on success, refreshEnvironments() + updateActiveEnvironmentPath(".venv/bin/python", <project>) via the MS Python extension API; degrades gracefully if the extension is absent.
• Three entry points, all triggering the same flow and reflecting the matched state on success:
  • command databricks.environment.setupVpex (+ databricks.environment.showVpexVersions)
  • a $(rocket) status-bar button
  • a node under the Python Environment tree section
• MsPythonExtensionWrapper — resolve uv from ~/.local/bin / ~/.cargo/bin / $XDG_BIN_HOME when it isn't on the extension-host PATH, so uv venvs no longer fall back to the (absent) native pip.

This is intentionally kept parallel to the existing databricks.environment.setup (FeatureManager) flow rather than merged into it.

Verification

• tsc --noEmit, eslint src, prettier: clean
• Unit suite (VS Code test host): 237 passing, 0 failing
• Ran the real databricks dbconnect init against a demo project: phases preflight → resolve → fetch → parse-python-version → plan → apply → ensure-python all ok; the final uv sync (PyPI-dependent) was blocked only by no network access in the test environment.

Backward compatibility

Additive: new commands, a new status-bar button, and a new tree node. The ConfigurationDataProvider constructor gains one parameter (internal). No changes to existing commands, settings, or persisted state/formats.

⚠️ Why this is do-not-merge

• The dbconnect subcommand currently exists only in the dev CLI build, so CLI_PATH is hardcoded to a local absolute path (marked DEMO/POC in code). This must switch to CliWrapper.cliPath once the bundled CLI ships dbconnect.
• serverless-v4 / Python 3.12 / databricks-connect 17.3 and macOS-only .venv/bin/python are hardcoded for the demo.

This pull request and its description were written by Isaac.

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• PR number: 1924
• Commit SHA: 6852bc9312d9b8d4b3992b8b53c8248aec84c40e

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