Add comprehensive CDP Embedded Wallets + Base Account integration guide

[Jnix2007]

summary

replaced the placeholder "coming soon" content in docs/base-account/framework-integrations/cdp.mdx with a comprehensive integration guide

updated content

• complete step-by-step implementation guide
• working code snippets for React hooks and components
• proper provider setup using CDPReactProvider + CDPHooksProvider

so what?

• removes outdated CDP Wagmi references
• uses CDP React provider approach for wallet persistence
• includes critical CORS config guidance
• provides production-ready code snippets

but did you test it?

built & tested a complete demo app following this guide to ensure all steps work correctly

[cb-heimdall]

✅ Heimdall Review Status

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Reviews	✅ 1/1	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 0 Sum 1