[feat](trx-protocol): create protocol unification crate
Add new crate to centralize protocol conversion logic:
- codec module: mode parsing/formatting, envelope parsing
- auth module: token validation, bearer prefix handling
- mapping module: ClientCommand <-> RigCommand conversion
Includes 76 comprehensive tests covering all command variants,
error cases, and round-trip conversions. Removes duplication
across listener, remote_client, and HTTP-JSON frontend.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>
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