docs: clarify notebook instructions

[vividvisit]

Problem

Polish instructional prose in three notebooks so setup steps and retrieval explanations read naturally.

Solution

The edits clarify initialization, programmatic configuration, returned results, matching criteria, and prerequisites without changing executable cells.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Infrastructure change (CI configs, etc)
• Non-code change (docs, etc)
• None of the above: (explain here)

Test Plan

Describe specific steps for validating this change.

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Note

Low Risk
Documentation-only typo and newline fixes with no runtime or API impact.

Overview
Polishes instructional prose in three example notebooks with spelling and formatting fixes only; no executable cells or behavior change.

In langchain-retrieval-agent.ipynb, corrects the Context API section heading (Receiving), feedback_bot docstring (criteria), and grading prompt text (necessary), and restores a proper trailing newline on the notebook JSON.

pinecone-quickstart.ipynb fixes initialize in the client setup step. quick-tour/namespacing.ipynb fixes programmatically in the multitenancy guidance.

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[vividvisit]

@jennapederson Could you please take a look when you have a chance? Thanks!