mcp: accept foreign absolute cwd for remote stdio (#29493)

## Why

Remote stdio MCP servers can run in an environment whose path convention
differs from the Codex host. A Windows cwd such as
`C:\Users\openai\share` is absolute for the executor but was rejected by
a POSIX orchestrator.

Built on #29501, now merged, which only clarifies the host-native
`PathUri` constructor name.

## What changed

- Deserialize MCP cwd values as `LegacyAppPathString` so config does not
apply host path rules.
- Interpret that spelling as host-native for local launches and convert
it to `PathUri` at executor launch.
- Skip host filesystem and command resolution checks for remote stdio in
`codex doctor`.
- Add host-independent config and executor-boundary coverage using the
foreign path convention for each test platform.

## Validation

- `just test -p codex-utils-path-uri -p codex-config -p codex-mcp -p
codex-rmcp-client` (408 passed)
- `just test -p codex-cli -p codex-rmcp-client` (372 passed)
- `cargo check --workspace --tests`
- `just test` (11,311 passed; 43 unrelated environment/timing failures)
- `just fix -p codex-cli -p codex-config -p codex-core -p codex-mcp -p
codex-mcp-extension -p codex-rmcp-client -p codex-tui`

codex-rs/cli/src/mcp_cmd.rs

@@ -640,7 +640,7 @@ async fn run_list(config_overrides: &CliConfigOverrides, list_args: ListArgs) ->
                 let env_display = format_env_display(env.as_ref(), env_vars);
                 let cwd_display = cwd
                     .as_ref()
-                    .map(|path| path.display().to_string())
+                    .map(ToString::to_string)
                     .filter(|value| !value.is_empty())
                     .unwrap_or_else(|| "-".to_string());
                 let status = format_mcp_status(cfg);
@@ -897,7 +897,7 @@ async fn run_get(config_overrides: &CliConfigOverrides, get_args: GetArgs) -> Re
             println!("  args: {args_display}");
             let cwd_display = cwd
                 .as_ref()
-                .map(|path| path.display().to_string())
+                .map(ToString::to_string)
                 .filter(|value| !value.is_empty())
                 .unwrap_or_else(|| "-".to_string());
             println!("  cwd: {cwd_display}");