Use ApiPathString in app-server filesystem permission paths (#28367)

## Why

Clients running an app-server on one OS and an exec-server on another OS
need to be able to pass sandbox config to app-server that refers to
resources on the executor's foreign OS.

## What

`AbsolutePathBuf` can't represent these paths and we don't want users to
be exposed to `PathUri` yet, so this moves the public app-server API to
be expressed in terms of `ApiPathString`.

Stacked on #28165.

- change app-server v2 filesystem permission paths, including legacy
read/write roots, to `ApiPathString`
- localize API paths through `PathUri` when converting into the current
native core permission types
- make path-bearing permission conversions fallible and surface
localization failures instead of silently treating malformed grants as
ordinary denials
- propagate conversion failures through app-server and TUI approval
handling
- regenerate the app-server JSON and TypeScript schemas
- leave migration TODOs on native-path conversions so they can be
removed once core permission paths use `PathUri`

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -3504,7 +3504,7 @@ mod tests {
             additional_permissions: Some(v2::AdditionalPermissionProfile {
                 network: None,
                 file_system: Some(v2::AdditionalFileSystemPermissions {
-                    read: Some(vec![absolute_path("/tmp/allowed")]),
+                    read: Some(vec![absolute_path("/tmp/allowed").into()]),
                     write: None,
                     glob_scan_max_depth: None,
                     entries: None,