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/analytics/src/analytics_client_tests.rs

@@ -105,6 +105,7 @@ fn sample_thread_start_response(thread_id: &str, ephemeral: bool, model: &str) -
             model_provider: "openai".to_string(),
             service_tier: None,
             cwd: PathBuf::from("/tmp"),
+            instruction_sources: Vec::new(),
             approval_policy: AppServerAskForApproval::OnFailure,
             approvals_reviewer: AppServerApprovalsReviewer::User,
             sandbox: AppServerSandboxPolicy::DangerFullAccess,
@@ -155,6 +156,7 @@ fn sample_thread_resume_response_with_source(
             model_provider: "openai".to_string(),
             service_tier: None,
             cwd: PathBuf::from("/tmp"),
+            instruction_sources: Vec::new(),
             approval_policy: AppServerAskForApproval::OnFailure,
             approvals_reviewer: AppServerApprovalsReviewer::User,
             sandbox: AppServerSandboxPolicy::DangerFullAccess,