refactor: trim icp-cli skill, add candid config

[marc0olo]

Summary

• Merge pitfall "Writing dfx.json instead of icp.yaml" into "Using dfx instead of icp" — removes redundancy, 9 pitfalls now
• Remove multi-canister config example — it was just Rust + Asset combined; replaced with a one-liner note
• Add candid recipe configuration to Rust and Motoko examples with correct semantics (if specified, file must exist; auto-generated when omitted)
• Add candid to dfx→icp configuration mapping table — addresses gap found in real-world testing (dfx.json conversion)