[refactor](trx-frontend-http-json): consolidate protocol logic with trx-protocol

Use centralized trx-protocol crate for:
- parse_mode and envelope parsing
- command mapping (ClientCommand -> RigCommand)
- token validation via RegistryTokenValidator wrapper

RegistryTokenValidator maintains compatibility with global auth
registry pattern while leveraging shared protocol logic from
trx-protocol. Removes duplicate auth and codec functions.

No behavior changes, all tests pass.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>

src/trx-client/trx-frontend/trx-frontend-http-json/Cargo.toml

@@ -10,6 +10,7 @@ edition = "2021"
 [dependencies]
 trx-core = { path = "../../../trx-core" }
 trx-frontend = { path = ".." }
+trx-protocol = { path = "../../../../src/trx-protocol" }
 tokio = { workspace = true, features = ["full"] }
 serde_json = { workspace = true }
 tracing = { workspace = true }