fix(accessibility): add descriptive alt text to onchainkit images

[Earnwithalee7890]

What changed? Why?

This PR enhances accessibility for the OnchainKit documentation by adding descriptive alt text to all images. The changes ensure that developers using screen readers and other assistive technologies can fully understand the visual examples, component demonstrations, and configuration screenshots that are essential to implementing OnchainKit components.

Files updated:

• docs/onchainkit/transaction/transaction.mdx - Enhanced alt text for Paymaster endpoint configuration screenshot and transaction component anatomy diagram
• docs/onchainkit/mint/nft-mint-card.mdx - Updated alt text for the NFT Mint Card checkout flow animation to describe the user interaction
• docs/onchainkit/wallet/wallet-modal.mdx - Improved alt text for the Wallet Modal screenshot to describe the connection options displayed

All alt text now provides clear, meaningful descriptions that help users understand:

• What UI components and interfaces look like
• The purpose and functionality shown in screenshots
• The structure and relationships in component diagrams
• Step-by-step flows in animated examples

Notes to reviewers

• All changes follow WCAG 2.1 Level AA accessibility guidelines
• Alt text describes both visual appearance and functional purpose
• Technical diagrams include explanations of component relationships
• No modifications to actual image files or code examples
• Documentation structure and functionality remain unchanged

How has it been tested?

• Manually verified each alt text accurately describes the image content and purpose
• Confirmed all images render correctly with updated alt attributes
• Reviewed alt text from the perspective of a developer using a screen reader
• Validated that all MDX syntax is correct and documentation builds successfully
• Checked that component examples and visual presentation remain intact

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/2	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2