Move the config schema generator into a dedicated crate (#41915)

## What changed

- Add the `codex-config-schema` workspace and Bazel crate for the
  `codex-write-config-schema` binary.
- Preserve `codex-rs/core/config.schema.json` as the default output location.
- Update `just write-config-schema` to run the new crate and remove the schema
  generator's `clap` dependency and binary target from `codex-core`.

GitOrigin-RevId: 7447f97d6e44d1077b16d2d850f8a8add9117ea6

codex-rs/core/Cargo.toml

@@ -8,10 +8,6 @@ version.workspace = true
 name = "codex_core"
 path = "src/lib.rs"
 
-[[bin]]
-name = "codex-write-config-schema"
-path = "src/bin/config_schema.rs"
-
 [lints]
 workspace = true
 
@@ -22,7 +18,6 @@ async-channel = { workspace = true }
 base64 = { workspace = true }
 bm25 = { workspace = true }
 chrono = { workspace = true, features = ["serde"] }
-clap = { workspace = true, features = ["derive"] }
 codex-analytics = { workspace = true }
 codex-agent-graph-store = { workspace = true }
 codex-agent-roles = { workspace = true }