feat: add explicit IdeaLoom Obsidian exchange

[atomantic]

Summary

• Add explicit configured-vault IdeaLoom Markdown import and export actions.
• Preserve list UUIDs, ordering, timestamps, imported note paths, and machine-local sync metadata.
• Surface malformed, duplicate, unavailable, failed, skipped, and conflicted exchange outcomes without overwriting ambiguous changes.
• Keep native Brain ideas and federation behavior separate from IdeaLoom lists.

Test plan

• npx vitest run services/idealoomObsidian.test.js services/idealoomLists.test.js routes/brain.test.js (133 passed)
• npx vitest run src/components/brain/IdeaLoomLists.test.jsx (9 passed)
• npm run lint in client (clean)

Closes #5338
Part of #5317