Update wallet release documentation for June 29 releases

Created by: ihsraham

Summary

• Add the June 29 changelog entries for wdk-wallet v1.0.0-beta.12, wallet-solana v1.0.0-beta.11, and wallet-ton-gasless v1.0.0-beta.7.
• Update shared wallet interface docs to remove ISigner.signTransaction() and clarify account-level signed transaction handling.
• Document Solana transactionMaxFee for native send/sign flows and clarify TON gasless fee-cap behavior and unsupported native transaction methods.
• Rename the TON gasless native-send navigation/card label to make the unsupported flow explicit.

Release Sources

• https://github.com/tetherto/wdk-wallet/releases/tag/v1.0.0-beta.12
• https://github.com/tetherto/wdk-wallet-solana/releases/tag/v1.0.0-beta.11
• https://github.com/tetherto/wdk-wallet-ton-gasless/releases/tag/v1.0.0-beta.7

Validation

• git diff --check
• npm run check:meta
• npm run check:redirects
• LINK_CHECK_EXTERNAL=false npm run check:links
• npm run build
• npm run quality before the final rebase; it passed with existing unrelated external-link warnings/redirect notices and existing unrelated SEO docType warnings.