Add Xquik MCP submit example

[kriptoburak]

Summary

• add a ready-to-edit Xquik JSON-RPC payload for the submit tool
• document payload validation with python3 -m json.tool before copying examples into requests
• clarify that submitters should use searchable descriptions and verify normalized entries with get
• remove two dead mcp-spider repository links so README link checks pass

Validation

• python3 -m json.tool examples/xquik-submit.json >/dev/null
• git diff --check
• npx --yes markdown-link-check README.md examples/README.md --quiet
• cargo test --manifest-path mcpub/Cargo.toml

Note: cargo fmt --manifest-path mcpub/Cargo.toml --check still reports pre-existing formatting drift in untouched Rust source, so I left code formatting out of this docs/listing patch.