[Workers AI] Add tutorial for AI-powered interview practice tool (#18049)

* [Workers AI] Add tutorial for AI-powered interview practice tool

* [Workers AI] Update content to follow the style guide recommendation

* refactor: change pronouns from first to second person

* Apply suggestions from code review

Co-authored-by: db-cloudflare <[email protected]>

* update route configuration with auth middleware

* Update src/content/docs/workers-ai/tutorials/build-ai-interview-practice-tool.mdx

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Co-authored-by: db-cloudflare <[email protected]>

Author: berezovyy