fix(accessibility): add descriptive alt text to mini apps images

[Earnwithalee7890]

What changed? Why?

This PR improves accessibility for the Mini Apps documentation by adding descriptive alt text to all images. The changes ensure that users relying on screen readers or assistive technologies can understand the content and purpose of each image.

Files updated:

• docs/mini-apps/quickstart/create-new-miniapp.mdx - Updated alt text for Account Association and Base app publishing screenshots
• docs/mini-apps/introduction/overview.mdx - Enhanced alt text for social feed animations and the builder flywheel diagram
• docs/mini-apps/core-concepts/embeds-and-previews.mdx - Improved alt text for the mini app preview embed screenshot
• docs/mini-apps/core-concepts/notifications.mdx - Updated alt text for the iPhone notification screenshot

All alt text now provides meaningful descriptions that convey the purpose and content of the images rather than generic labels.

Notes to reviewers

• Alt text changes follow WCAG 2.1 accessibility guidelines
• Descriptions are concise but informative
• Each alt text provides context about what the image shows and its purpose in the documentation
• No functional changes to the documentation content itself

How has it been tested?

• Manually reviewed all alt text changes for clarity and accuracy
• Verified that alt text accurately describes the visual content
• Confirmed that the documentation still renders correctly with the updated alt attributes
• Checked that alt text provides sufficient context for users who cannot see the images

[cb-heimdall]

🟡 Heimdall Review Status

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