Extract MCP into codex-mcp crate (#15919)

- Split MCP runtime/server code out of `codex-core` into the new
`codex-mcp` crate. New/moved public structs/types include `McpConfig`,
`McpConnectionManager`, `ToolInfo`, `ToolPluginProvenance`,
`CodexAppsToolsCacheKey`, and the `McpManager` API
(`codex_mcp::mcp::McpManager` plus the `codex_core::mcp::McpManager`
wrapper/shim). New/moved functions include `with_codex_apps_mcp`,
`configured_mcp_servers`, `effective_mcp_servers`,
`collect_mcp_snapshot`, `collect_mcp_snapshot_from_manager`,
`qualified_mcp_tool_name_prefix`, and the MCP auth/skill-dependency
helpers. Why: this creates a focused MCP crate boundary and shrinks
`codex-core` without forcing every consumer to migrate in the same PR.

- Move MCP server config schema and persistence into `codex-config`.
New/moved structs/enums include `AppToolApproval`,
`McpServerToolConfig`, `McpServerConfig`, `RawMcpServerConfig`,
`McpServerTransportConfig`, `McpServerDisabledReason`, and
`codex_config::ConfigEditsBuilder`. New/moved functions include
`load_global_mcp_servers` and
`ConfigEditsBuilder::replace_mcp_servers`/`apply`. Why: MCP TOML
parsing/editing is config ownership, and this keeps config
validation/round-tripping (including per-tool approval overrides and
inline bearer-token rejection) in the config crate instead of
`codex-core`.

- Rewire `codex-core`, app-server, and plugin call sites onto the new
crates. Updated `Config::to_mcp_config(&self, plugins_manager)`,
`codex-rs/core/src/mcp.rs`, `codex-rs/core/src/connectors.rs`,
`codex-rs/core/src/codex.rs`,
`CodexMessageProcessor::list_mcp_server_status_task`, and
`utils/plugins/src/mcp_connector.rs` to build/pass the new MCP
config/runtime types. Why: plugin-provided MCP servers still merge with
user-configured servers, and runtime auth (`CodexAuth`) is threaded into
`with_codex_apps_mcp` / `collect_mcp_snapshot` explicitly so `McpConfig`
stays config-only.

codex-rs/codex-mcp/Cargo.toml

@@ -0,0 +1,40 @@
+[package]
+edition.workspace = true
+license.workspace = true
+name = "codex-mcp"
+version.workspace = true
+
+[lib]
+name = "codex_mcp"
+path = "src/lib.rs"
+
+[lints]
+workspace = true
+
+[dependencies]
+anyhow = { workspace = true }
+async-channel = { workspace = true }
+codex-async-utils = { workspace = true }
+codex-config = { workspace = true }
+codex-login = { workspace = true }
+codex-otel = { workspace = true }
+codex-plugin = { workspace = true }
+codex-protocol = { workspace = true }
+codex-rmcp-client = { workspace = true }
+codex-utils-plugins = { workspace = true }
+futures = { workspace = true }
+regex-lite = { workspace = true }
+rmcp = { workspace = true, default-features = false, features = ["base64", "macros", "schemars", "server"] }
+serde = { workspace = true, features = ["derive"] }
+serde_json = { workspace = true }
+sha1 = { workspace = true }
+thiserror = { workspace = true }
+tokio = { workspace = true, features = ["macros", "rt-multi-thread"] }
+tokio-util = { workspace = true, features = ["rt"] }
+tracing = { workspace = true }
+url = { workspace = true }
+
+[dev-dependencies]
+pretty_assertions = { workspace = true }
+rmcp = { workspace = true, default-features = false, features = ["base64", "macros", "schemars", "server"] }
+tempfile = { workspace = true }