Refactor: rename contact samples to custom-components-example

[dmandar]

Description

Renamed the agent and the client to something clearer. Will have a separate MCP apps only sample.

Pre-launch Checklist

• [ X] I signed the CLA.
• [ X] I read the Contributors Guide.
• [ X] I read the Style Guide.
• [ X] I have added updates to the CHANGELOG.
• [ X] I updated/added relevant documentation.
• [ X] My code changes (if any) have tests.

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[gemini-code-assist]

Code Review

This pull request renames the "contact" and "contact_multiple_surfaces" sample to "custom-components-example" across the agent and client codebases, updating documentation, workspace configurations, and test paths. The review feedback identifies several remaining inconsistencies where the old naming or descriptions are still present, specifically within the test catalog configurations, the Python package name in the lock file (which requires a change in pyproject.toml), and the npm package description.