Add WebRTC media transport to realtime TUI (#17058)

Adds the `[realtime].transport = "webrtc"` TUI media path using a new
`codex-realtime-webrtc` crate, while leaving app-server as the
signaling/event source.\n\nLocal checks: fmt, diff-check, dependency
tree only; test signal should come from CI.

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Co-authored-by: Codex <noreply@openai.com>

codex-rs/cli/Cargo.toml

@@ -3,6 +3,7 @@ name = "codex-cli"
 version.workspace = true
 edition.workspace = true
 license.workspace = true
+build = "build.rs"
 
 [[bin]]
 name = "codex"