feat(python-notebook-migration, frontend): add AI-generate-workflow modal, panel host, and LLM loading spinner

[zyratlo]

What changes were proposed in this PR?

Introduces the user-facing entry point for the Python-notebook to Texera-workflow migration tool: an "AI Generate Workflow from Python Notebook" modal in the workspace menu, a workspace-level loading overlay with an elapsed-time stopwatch that shows while the LLM is converting, and the <texera-jupyter-notebook-panel> host that places the iframe panel landed in migration-tool-jupyter-panel into the workspace.

menu.component.{ts,html}

• Adds a public get pythonNotebookMigrationEnabled(): boolean getter on MenuComponent that returns config.env.pythonNotebookMigrationEnabled
• Adds an @Output() setWaitingForLLM = new EventEmitter<boolean>() that the workspace component consumes to gate the loading overlay.
• Adds importForm: FormGroup (description, file with required validator, model, apiKey) and a ViewChild reference to #importNotebookModal.
• openImportNotebookModal() opens an NzModalService modal; loads the model dropdown via notebookMigrationService.getAvailableModels().
• beforeUpload(file) patches the chosen file into the form without triggering an auto-upload.
• onClickImportNotebook(file, model, apiKey) is the main action.
  • Validates the .ipynb extension
  • emits setWaitingForLLM(true)
  • reads the file
  • tags every code cell with a UUID in metadata.uuid
  • calls sendNotebookToJupyter(...) (so the user can see the notebook in the embedded JupyterLab
  • calls sendToAIGenerateWorkflow(...)
    • persists the result via workflowPersistService.persistWorkflow(...)
  • calls notebookMigrationService.storeNotebookAndMapping(...) to persist the mapping in Postgres
  • reloads the workflow via workflowActionService.reloadWorkflow(...)
  • opens the iframe panel via jupyterPanelService.openPanel("JupyterNotebookPanel")
  • Emits setWaitingForLLM(false) in finally.
• HTML
  • adds the AI Generate button (gated on *ngIf="pythonNotebookMigrationEnabled")
  • adds the modal template #importNotebookModal popup diagram image

workspace.component.{ts,html,scss} — panel host + loading overlay:

• TS adds isWaitingForLLM: boolean, timerInterval, startTime, the onWaitingForLLMChanged(isWaiting) handler bound to the menu's output, startTimer / stopTimer / updateElapsedTime helpers, and a formattedElapsedTime getter that returns mm:ss.
• HTML adds the <texera-jupyter-notebook-panel> host (which subscribes to the visibility surface added in migration-tool-panel-controls to know when to render) and the loading overlay (*ngIf="isWaitingForLLM")

Image asset:

• frontend/src/assets/notebook_migration_tool/tool_popup_diagram.png
  • diagram embedded at the top of the modal that walks the user through what the tool does.

Any related issues, documentation, discussions?

Closes #4427
Parent issue #4301

How was this PR tested?

Manual end-to-end on a branch where all the dep PRs were merged: enabled the flag, opened the workspace menu, clicked AI Generate Workflow, picked a sample .ipynb, picked a LiteLLM model, entered an API key, and watched the spinner tick up while the conversion ran. After ~30s the workflow appeared in the editor with PythonUDFV2 operators in place, the panel auto-opened with the notebook visible in the embedded JupyterLab, and clicking an operator scrolled the corresponding notebook cell into view. Clicking a cell highlighted its corresponding operators.

Was this PR authored or co-authored using generative AI tooling?

Generated-by: Claude Code (Claude Opus 4.7)

[codecov-commenter]

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