fix(storage): import Codex item_completed messages

[sunrioa]

Summary

• Read Codex 0.149 event_msg.item_completed records for UserMessage, Reasoning, and AgentMessage.
• Preserve message IDs, turn IDs, timestamps, and active model metadata.
• Derive imported-session titles from completed user items while retaining support for the legacy user_message and agent_* event shapes.
• Continue treating event_msg as the presentation-message source so that corresponding response_item mirrors are not imported twice.
• Add a sanitized Codex 0.149 regression fixture covering title discovery, message conversion, terminal state, canonical decoding, and duplicate suppression.

Fixes #3516
Refs #2499

Verification

• Focused codex-session-adapter suite: 9 passed.
• NODE_NO_WARNINGS=1 npm --workspace @maka/storage run test:dist: 899 passed, 14 skipped.
• npm run lint
• npm run format:check
• npm run build
• npm run typecheck
• npm run check:asf-headers
• git diff --check
• Real rollout conversion smoke test restored 1 user message, 2 assistant messages, and 1 terminal turn-state message without importing response mirrors twice.
• Before-fix evidence and environment details are available in Codex Desktop 0.149 conversations import with an empty transcript #3516.

Without NODE_NO_WARNINGS=1, one unrelated managed-dependency environment test treats Node.js's experimental node:sqlite warning on child-process stderr as a failure. The full storage suite passes when that warning is disabled.

Review focus

The adapter keeps the legacy and Codex 0.149 presentation formats side by side. event_msg remains the authority for user, reasoning, and assistant presentation messages, while response_item remains responsible for tool calls and tool results. This preserves the existing duplicate-prevention boundary.

AI use

Select exactly one:

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

Tool(s) and scope:

OpenAI Codex assisted with the rollout-format investigation, implementation, regression tests, local verification, and drafting this description. I reproduced the issue and reviewed the final diff, regression coverage, and test results before submission.

Checklist

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

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No