Expose instruction sources (AGENTS.md) via app server (#17506)

Addresses #17498

Problem: The TUI derived /status instruction source paths from the local
client environment, which could show stale <none> output or incorrect
paths when connected to a remote app server.

Solution: Add an app-server v2 instructionSources snapshot to thread
start/resume/fork responses, default it to an empty list when older
servers omit it, and render TUI /status from that server-provided
session data.

Additional context: The app-server field is intentionally named
instructionSources rather than AGENTS.md-specific terminology because
the loaded instruction sources can include global instructions, project
AGENTS.md files, AGENTS.override.md, user-defined instruction files, and
future dynamic sources.

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

@@ -27,6 +27,7 @@ pub(crate) struct PendingThreadResumeRequest {
     pub(crate) request_id: ConnectionRequestId,
     pub(crate) rollout_path: PathBuf,
     pub(crate) config_snapshot: ThreadConfigSnapshot,
+    pub(crate) instruction_sources: Vec<PathBuf>,
     pub(crate) thread_summary: codex_app_server_protocol::Thread,
 }