Onboard: O-P3 tour state & persistence (QSettings + cloud sync)

[fernandotonon]

Part of #806 — Onboard: guided tours (editor). Depends on O-P1/O-P2.

Goal

Persist which tours the user has seen and, when signed in, share that state with the web client.

Work

• Local: QSettings group tours/<id> → { status, step, version, at } (status = completed|dismissed|in_progress). Survives restarts.
• Cloud sync: when logged in (reuse QtMeshCloudSession), sync via GET/PUT /v1/me/tours (the endpoint from web T-P2), merging local + remote so a tip dismissed on the website doesn't reappear in the editor (and vice-versa).
• Version-aware: a bumped tour version may re-show once; same version never re-nags after completion/dismissal.

Acceptance criteria

• Completed/dismissed tours don't auto-show again (same version), across restarts.
• When logged in, state round-trips through /v1/me/tours and merges with local.
• Bumping a version allows a one-time re-show.
• Works fully offline (local-only), syncing when a session is available.