Agent Skills: convert-elixir-erlang

Bidirectional conversion between Elixir and Erlang. Use when migrating projects between these languages in either direction. Extends meta-convert-dev with Elixir↔Erlang specific patterns. Use when migrating Elixir projects to Erlang, translating Elixir patterns to Erlang idioms, or refactoring Elixir codebases to Erlang. Both run on the BEAM VM with the same OTP framework, making this conversion primarily syntactic with semantic preservation. Extends meta-convert-dev with Elixir-to-Erlang specific patterns.