app-server: move transport into dedicated crate

[euroelessar]

Why

codex-app-server currently owns both request-processing code and transport implementation details. Splitting the transport layer into its own crate makes that boundary explicit, reduces the amount of transport-specific dependency surface carried by codex-app-server, and gives future transport work a narrower place to evolve.

What changed

• Added codex-app-server-transport and moved the existing transport tree into it, including stdio, unix socket, websocket, remote-control transport, and websocket auth.
• Moved shared transport-facing message types into the new crate so both the transport implementation and codex-app-server use the same definitions.
• Kept processor-facing connection state and outbound routing in codex-app-server, with the routing tests moved next to that local wrapper.
• Updated workspace metadata, Bazel crate metadata, and codex-app-server dependencies for the new crate boundary.

Validation

• cargo metadata --locked --no-deps
• git diff --check
• Attempted cargo test -p codex-app-server-transport, cargo test -p codex-app-server, just fix -p codex-app-server-transport, and just fix -p codex-app-server; all were blocked before compilation by the existing packageproxy resolution failure for locked rustls-webpki = 0.103.13.
• Attempted Bazel build / lockfile validation; those were blocked by external fetch failures against BuildBuddy / GitHub while resolving v8.

[chatgpt-codex-connector]

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