fix(codex-integration): context row now persists

[StuBehan]

Summary

The Codex context-usage row in the Sessions tab (and the compact pill) disappeared after navigating away and back, or once enough new events accumulated. This makes it persist: Codex now resolves its context stats through a stable per-PID transcript handle that the poll re-reads, instead of the prunable event list — matching how Claude already behaves.

Changes

Root cause: Codex has no per-pid session sidecar like Claude (~/.claude/sessions/<pid>.json), so session.claudeSessionID is nil and the views fell back to scanning EventStore for a matching event to find the stats key. EventStore prunes to maxEventsTotal=100 / maxEventsPerSession=5, so once enough newer events arrive the Codex Stop event ages out and the lookup returns nil → the row vanishes. The compact pill had no event fallback at all, so Codex never showed context there.

Fix:

• Add TranscriptRef { sessionID, path } and PanelNav.transcriptRefByPID: [Int: TranscriptRef] — a stable per-agent-PID handle to a transcript, held on nav (survives panel navigation and event pruning).
• Populate the cache from each Codex hook event (refreshTranscriptStats), keyed by agent PID.
• Add a Codex branch to the poll refresh (refreshAllClaudeStats): for active non-Claude sessions with a cached ref, re-read the transcript path so stats stay live and repopulate — mirroring Claude's sidecar-driven refresh.
• Resolve Codex stats via the PID cache in both Sessions.swift and CompactView.swift (the pill previously had no fallback).

Resulting behavior: the PID→path binding persists; stats are re-read from the live rollout file on each poll while the session is active; a transient read failure keeps the last value rather than blanking. Claude is unaffected (it still hits its claudeSessionID path first).

Testing

• swift build — clean.
• ./build.sh — full app builds.
• Not exercisable in CI (panel/AX + live transcript). Manually verified on macOS: with a live Codex session, the context row now persists across tab navigation and panel close/reopen (previously it disappeared once the source event was pruned).

Related issues

None.