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-protocol/src/protocol/common.rs

@@ -1405,6 +1405,7 @@ mod tests {
                 model_provider: "openai".to_string(),
                 service_tier: None,
                 cwd: PathBuf::from("/tmp"),
+                instruction_sources: vec![PathBuf::from("/tmp/AGENTS.md")],
                 approval_policy: v2::AskForApproval::OnFailure,
                 approvals_reviewer: v2::ApprovalsReviewer::User,
                 sandbox: v2::SandboxPolicy::DangerFullAccess,
@@ -1444,6 +1445,7 @@ mod tests {
                     "modelProvider": "openai",
                     "serviceTier": null,
                     "cwd": "/tmp",
+                    "instructionSources": ["/tmp/AGENTS.md"],
                     "approvalPolicy": "on-failure",
                     "approvalsReviewer": "user",
                     "sandbox": {