docs(base-account): fix broken README links in demo templates

[dieutx]

Summary

Two Base Account demo template READMEs contain broken links.

Broken links

• base-account/base-account-privy-template/README.md links to LICENSE in the local directory, but the file only exists at the repo root.
• base-account/base-account-rainbow-template/README.md links to a GitHub GUIDE.md path that does not exist.

Suggested fix

• point the Privy template README to the repo-root license file
• replace the missing RainbowKit guide link with existing documentation links