Add docs/examples.md prompt cookbook

[dkijania]

Why

The README has exactly one worked example (end-to-end payment in tutorial mode). That undersells what the server can do — and the more curated example prompts a user sees, the faster they can spot the one closest to their use case.

A handful of natural-language prompts that drive multi-tool sequences end-to-end would double as:

1. Documentation — concrete starting points for new users.
2. Regression seed — feed them through the server periodically and check the LLM still completes them.

Scope

• Add `docs/examples.md` (or `examples/` directory) covering at least:
  • Devnet payment with dry-run → commit → poll
  • Tutorial lifecycle with faucet accounts
  • Multi-wallet orientation (`describe_state` + `get_account` per wallet)
  • GraphQL vs Rosetta cross-validation
  • Archive top-10 accounts query (SQL via `query_archive_sql`)
  • zkApp event/action walk-through
  • Multi-network sync-status sanity check
  • Mempool watch grouped by source account
  • Funding handoff flow
  • Pre-deploy smoke test across all live networks
• Each example: one-line goal, the natural-language prompt, expected tool sequence, expected final output.
• Link from the README's top-level "Features" section so users hit it early.

Acceptance

• A new user can pick an example closest to their goal, paste the prompt verbatim into their MCP client, and get a sensible result.
• The example list is referenced by #(LLM-friendliness audit issue) as the measurement corpus.