docs(core): document HTTP QUERY operation

[soyuka]

Documents the HTTP QUERY operation from RFC 10008.

• explains request-body criteria, required Content-Type, and supported media types
• covers parameter-driven filters and criteria DTOs without implying provider-side DTO injection
• documents the explicit deserialize/write/processor path for typed criteria
• describes the OpenAPI 3.2 query Path Item field

Checks: npx prettier --check core/operations.md; proselint core/operations.md; hugo --minify