feat: pass helper executable paths via Arg0DispatchPaths (#12719)

## Why

`codex-rs/core/src/tools/runtimes/shell/unix_escalation.rs` previously
located `codex-execve-wrapper` by scanning `PATH` and sibling
directories. That lookup is brittle and can select the wrong binary when
the runtime environment differs from startup assumptions.

We already pass `codex-linux-sandbox` from `codex-arg0`;
`codex-execve-wrapper` should use the same startup-driven path plumbing.

## What changed

- Introduced `Arg0DispatchPaths` in `codex-arg0` to carry both helper
executable paths:
  - `codex_linux_sandbox_exe`
  - `main_execve_wrapper_exe`
- Updated `arg0_dispatch_or_else()` to pass `Arg0DispatchPaths` to
top-level binaries and preserve helper paths created in
`prepend_path_entry_for_codex_aliases()`.
- Threaded `Arg0DispatchPaths` through entrypoints in `cli`, `exec`,
`tui`, `app-server`, and `mcp-server`.
- Added `main_execve_wrapper_exe` to core configuration plumbing
(`Config`, `ConfigOverrides`, and `SessionServices`).
- Updated zsh-fork shell escalation to consume the configured
`main_execve_wrapper_exe` and removed path-sniffing fallback logic.
- Updated app-server config reload paths so reloaded configs keep the
same startup-provided helper executable paths.

## References

- [`Arg0DispatchPaths`
definition](e355b43d5c/codex-rs/arg0/src/lib.rs (L20-L24))
- [`arg0_dispatch_or_else()` forwarding both
paths](e355b43d5c/codex-rs/arg0/src/lib.rs (L145-L176))
- [zsh-fork escalation using configured wrapper
path](e355b43d5c/codex-rs/core/src/tools/runtimes/shell/unix_escalation.rs (L109-L150))

## Testing

- `cargo check -p codex-arg0 -p codex-core -p codex-exec -p codex-tui -p
codex-mcp-server -p codex-app-server`
- `cargo test -p codex-arg0`
- `cargo test -p codex-core tools::runtimes::shell::unix_escalation:: --
--nocapture`

codex-rs/app-server/src/lib.rs

@@ -1,5 +1,6 @@
 #![deny(clippy::print_stdout, clippy::print_stderr)]
 
+use codex_arg0::Arg0DispatchPaths;
 use codex_cloud_requirements::cloud_requirements_loader;
 use codex_core::AuthManager;
 use codex_core::config::Config;
@@ -12,7 +13,6 @@ use std::collections::HashMap;
 use std::collections::HashSet;
 use std::io::ErrorKind;
 use std::io::Result as IoResult;
-use std::path::PathBuf;
 use std::sync::Arc;
 use std::sync::RwLock;
 use std::sync::atomic::AtomicBool;
@@ -291,13 +291,13 @@ fn log_format_from_env() -> LogFormat {
 }
 
 pub async fn run_main(
-    codex_linux_sandbox_exe: Option<PathBuf>,
+    arg0_paths: Arg0DispatchPaths,
     cli_config_overrides: CliConfigOverrides,
     loader_overrides: LoaderOverrides,
     default_analytics_enabled: bool,
 ) -> IoResult<()> {
     run_main_with_transport(
-        codex_linux_sandbox_exe,
+        arg0_paths,
         cli_config_overrides,
         loader_overrides,
         default_analytics_enabled,
@@ -307,7 +307,7 @@ pub async fn run_main(
 }
 
 pub async fn run_main_with_transport(
-    codex_linux_sandbox_exe: Option<PathBuf>,
+    arg0_paths: Arg0DispatchPaths,
     cli_config_overrides: CliConfigOverrides,
     loader_overrides: LoaderOverrides,
     default_analytics_enabled: bool,
@@ -548,7 +548,7 @@ pub async fn run_main_with_transport(
         let loader_overrides = loader_overrides_for_config_api;
         let mut processor = MessageProcessor::new(MessageProcessorArgs {
             outgoing: outgoing_message_sender,
-            codex_linux_sandbox_exe,
+            arg0_paths,
             config: Arc::new(config),
             single_client_mode,
             cli_overrides,