Agent Skills: convert-erlang-roc

Bidirectional conversion between Erlang and Roc. Use when migrating projects between these languages in either direction. Extends meta-convert-dev with Erlang↔Roc specific patterns. Use when migrating Erlang projects to Roc, translating BEAM/OTP patterns to functional patterns, or refactoring Erlang codebases. Extends meta-convert-dev with Erlang-to-Roc specific patterns.