Add Developer Knowledge API demo

[antfitch]

This is a demo which shows builders how to access Google product documentation in markdown format through Google's Developer Knowledge API.

[antfitch]

@joefspiro can you take a look at this?

[gemini-code-assist]

Code Review

This pull request introduces a Developer Knowledge API demo application built with Next.js, featuring documentation search, local user profile management via SQLite WASM, and specialized markdown rendering. Feedback indicates that using server actions to write API keys to .env.local is unsuitable for production environments and suggests using secure cookies or a database instead. Furthermore, the search API route should be updated to validate the presence of the API key and return a 401 Unauthorized response if it is missing.

[antfitch]

@joefspiro this is ready for another review. There is a blocking issue in another demo, agents/aicamp/osquery_data which someone needs to resolve.