Add gcloud authentication prerequisites to Cloud Run deployment guide

[selamw1]

Description

Adds a Prerequisites section to the Cloud Run deployment README.md to guide users through setting up authentication and enabling APIs before running the deploy.sh script. This prevents script failures due to missing active credentials or disabled APIs.

The guide now covers:

1. Authenticating via gcloud auth login.
2. Setting up Application Default Credentials via gcloud auth application-default login.
3. Enabling required run.googleapis.com and discoveryengine.googleapis.com APIs.

Fixes #1271

Pre-launch Checklist

• I signed the [CLA].
• I read the [Contributors Guide].
• I read the [Style Guide].
• I have added updates to the [CHANGELOG].
• I updated/added relevant documentation.
• My code changes (if any) have tests.
• If my branch is on fork, I have verified that scripts/e2e_test.sh passes.

[gemini-code-assist]

Code Review

This pull request modifies the CSS reset in the React renderer to exclude SVG elements and their descendants, restoring proper SVG rendering. It also adds a new unit test and updates the CHANGELOG. In the documentation, a prerequisites section was added to the Cloud Run sample README. Feedback highlights a major issue where a large portion of the README was accidentally deleted and a code block was left unclosed. Additionally, the reviewer noted a mismatch between the PR description and the functional changes, an incorrect issue reference in the CHANGELOG, and suggested improving the unit test by verifying computed styles.