🎨 Palette: Add descriptive alt text to architecture diagrams

[google-labs-jules]

I have improved the accessibility of the project documentation by adding descriptive alt text to the architecture diagrams in all template files.

💡 What: Added meaningful alt text to architecture diagrams in docs/template/*.md.
🎯 Why: Previously, these diagrams used empty alt text ![](), making them inaccessible to screen reader users.
♿ Accessibility: Screen reader users can now understand the relationships between AWS services (e.g., API Gateway -> Lambda -> DynamoDB) as depicted in the architecture diagrams.

Changes:

• Added alt text to agent.md, api.md, eventbridge.md, graphql.md, s3.md, sqs.md, and stream.md.
• Verified changes by running make lint and make test.
• Recorded UX learning in .Jules/palette.md.

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PR created automatically by Jules for task 17535745363249782501 started by @amrabed

[google-labs-jules]

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[amrabed]

LGTM