fix(storage): import current Codex transcript messages

[liugddx]

Summary

• Parse current Codex event_msg.item_completed presentation items into native Maka user and assistant messages.
• Keep the legacy presentation-event path authoritative when present so transitional/provider mirrors cannot duplicate visible content.
• Use current-format user presentation items for filesystem-fallback titles while ignoring injected provider context.

Root cause

Current Codex rollouts no longer emit the legacy user_message / agent_message events consumed by Maka. They emit item_completed with UserMessage / AgentMessage instead. Maka therefore imported tool calls, tool results, and turn states but zero visible user or assistant messages.

Verification

• npm run build -w @maka/storage — passed
• Codex adapter suite — 9 tests passed
• npm run lint — 2618 files passed
• npm run format:check — 1595 files passed
• Real current-format Codex rollouts converted with non-empty visible messages
• Maka Dev re-import rendered 2 user messages and 6 assistant messages for a previously empty imported Session

Screenshots are not applicable because this changes storage conversion rather than visual styling; the imported transcript was inspected in the running desktop app.

AI use

Select exactly one:

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: Codex diagnosed the schema drift against local rollout structure, implemented the compatibility parser and regression fixture, and performed adapter plus live desktop verification.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck/build and the affected suite pass locally

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No

[liugddx]

Closing in favor of #3520, which provides the more complete Codex item_completed import implementation and shared fixture coverage. I’ll continue review on #3520.