docs: migrate Base Account and Base MCP docs to CDP

[youssefea]

Summary

• remove the Base Account SDK and Base MCP sections, source pages, and unused demo snippets from Base docs
• add a Migrated Documentation page that points readers to Coinbase Wallet SDK and Wallet MCP on Coinbase Developer Platform
• redirect every former Base Account and Base MCP route to the single migration page
• update remaining cross-links, simplify the SDKs & APIs overview, remove Builder Codes from that page, and regenerate the AI-facing docs indexes

Supersedes #1915 with the current product names, destinations, and complete source migration.

Validation

• npm test
• node scripts/validate-docs-structure.js
• node scripts/check-terminology.js
• node scripts/lint-mdx.js --files-from=/tmp/changed-docs-final.txt --check-nav (0 errors; existing advisory code-block warnings only)
• mintlify dev at http://localhost:3000
• verified the migration page and SDK overview locally
• verified former /sdks/base-account/*, /base-account/*, /agents/*, and legacy /ai-agents/* routes resolve to /sdks/migrated-products

[mintlify]

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Project	Status	Preview	Updated
base	🟢 Ready	View Preview	Sep 11, 2026, 10:35 AM

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[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
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