Add 'building with AI' guidance to docs.miden.xyz

Source: DevEx Sync (Notion).

Two distinct AI-doc surfaces were identified, and the docs site does not yet cover either:

1. **Building *with* AI** — using Claude (and similar agents) to generate Miden code / interact with Miden tooling. The capability exists internally but is not discoverable to developers.
2. **Building *for* AI / using AI in Miden** — agentic flows on Miden itself (Philipp's agentic-template line of work, separately tracked for v15).

This issue is the placeholder to discuss and close the gap on **(1)**: surface "build with AI" guidance in `docs.miden.xyz` (e.g. a Tools or Get Started page covering Claude prompts, MCP server, recommended patterns, links to agentic-template once it's ready).

Owners per meeting: Brian + Philipp to discuss; this issue is the agreed-upon discussion thread.