[CLEAN] Synthetic Benchmark PR #20065 - Add V2 UI packaging and Docker integration

[tomerqodo]

Benchmark PR PrefectHQ#20065

Type: Clean (correct implementation)

Original PR Title: Add V2 UI packaging and Docker integration
Original PR Description: Related to PrefectHQ#15512

This PR adds support for building and serving the experimental V2 React UI alongside the existing V1 Vue UI in Docker images and Python packages.

The V2 UI can be enabled by setting PREFECT_SERVER_UI_V2_ENABLED=true when starting the server. V1 remains the default.

Changes:

• Add base path placeholder support to V2 vite.config.ts for dynamic serving
• Add new PREFECT_SERVER_UI_V2_ENABLED setting (default: false) to switch between UIs
• Add V2 UI path constants (__ui_v2_static_path__, __ui_v2_static_subpath__)
• Update Dockerfile with separate V2 UI builder stage using Node 22
• Update pyproject.toml to include ui-v2 as a build artifact
• Update create_ui_app() to serve the appropriate UI based on setting
• Update GitHub Actions workflow to build V2 UI

🤖 Generated with Claude Code
Original PR URL: PrefectHQ#20065