Update the Assistant quickstart notebook to Python SDK v10

[nicoalba10]

The Assistant quickstart notebook is linked from the Pinecone Assistant SDK quickstart and the docs' Assistant examples page. It installs the latest SDK, which is now v10, but its code predates v10, so it breaks partway through.

Fixes

• The chat cell imported Message from pinecone_plugins, which v10 doesn't ship, so it crashed with an ImportError.
• The evaluation cell was missing a closing parenthesis.
• Clean up deleted example-assistant with a placeholder key, but the notebook creates quickstart-assistant.
• Readers had to download the PDF and upload it to Colab by hand. The notebook now downloads it.

Changes

• Uses the current v10 calls (pc.assistants.create, upload_file, list_files, chat, context, and delete) and pins pinecone==10.0.0 and pinecone-notebooks==0.1.1.
• Uses the repo's standard API key helper: environment variable, then the Colab widget, then a prompt.
• Matches the updated docs quickstart: same steps and sample file, and the paid-only evaluation step moves to Next steps.
• Adds an intro and prerequisites, fixes the duplicate step 3, and prints answers and citations instead of raw response objects.

I ran the notebook top to bottom with this repo's CI runner (.github/actions/run-notebook/run-notebook.py) against the live API. It passed and cleaned up after itself.

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Note

Low Risk
Documentation-only notebook changes with no production code; main risk is readers following outdated API patterns if something was missed.

Overview
Rewrites docs/assistant-quickstart.ipynb so it runs end-to-end on Pinecone Python SDK v10, matching the linked docs quickstart.

The notebook now pins pinecone==10.0.0 and pinecone-notebooks==0.1.1, uses the pc.assistants.* surface (create, upload_file, list_files, chat, context, delete) instead of the old pc.assistant / plugin Message types, and chats with plain {"role", "content"} message dicts. Setup adds a shared get_pinecone_api_key() helper (env → Colab auth → prompt).

Upload downloads the sample Netflix 10-K in-notebook (with a User-Agent header), waits for processing, and uses richer sample metadata. Outputs are trimmed to readable answer/citation/snippet lines instead of huge pprint blobs. The in-notebook evaluation REST call is removed and called out under Next steps; cleanup deletes quickstart-assistant via the same assistant_name variable.

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