Show Codex sessions as Waiting when user action is required

[calvintvu]

Context

Codex sessions can remain Active while they wait for a user response or command approval. This change marks those sessions as Waiting until the user responds or the approval completes.

Changes

• Mark an open Codex turn as Waiting for an unanswered request_user_input call.
• Mark an open Codex turn as Waiting for a pending sandbox approval.
• Clear Waiting after an answer, completed approval, or newer user message.
• Keep sessions Active for saved approval rules and ordinary commands.

Test

• go test parse.go source.go fork.go types.go metadata.go discovery.go waiting_test.go — passed
• go build ./... — passed
• git diff --check origin/main...HEAD — passed
• Manual: An unanswered request_user_input prompt showed Waiting.

Screenshots

• Session board — Codex session shows Waiting during an unanswered question.

• Session board — Codex session shows Waiting during a pending approval.

[milanshen]

Three status-correctness findings.