Agent Skills: add-language

Guide for implementing a new language parser in Codanna. Use when adding language support, implementing parsers, or extending language capabilities. Covers the six-file architecture (mod.rs, definition.rs, parser.rs, behavior.rs, resolution.rs, audit.rs), trait implementation patterns, resolution scope design, and integration workflow. Triggers on requests to add language support, implement new parser, extend language capabilities, or create language implementation.