[Roadmap 15] Build desktop-only import bridge and review UI

[Fredoq]

What

Implement the Electron folder selection bridge and shared UI for reviewing import sessions and draft releases/tracks against the hosted Cratebase API.

Why

Local folder import is the practical path from existing music folders into hosted Cratebase, but filesystem access must stay desktop-only and reviewable. The desktop app is a hosted-account companion, not a separate local-first product in v1.

Scope

• Add or harden a narrow preload bridge with context isolation and no node integration in the renderer.
• Implement desktop-only folder selection and metadata scan handoff to the hosted authenticated API over HTTPS.
• Keep development overrides for local API testing without making self-hosting the v1 distribution path.
• Build import review screens shared with browser where possible.
• Test desktop/web import mode differences and preload bridge contracts.

Done when

• Desktop users can select a local folder and create an import session in their hosted account.
• Browser users can review existing sessions but cannot browse arbitrary local folders.
• The UI makes confirmation explicit before catalog writes.
• No audio files are uploaded by the desktop import flow.

Roadmap order

15 of 23.

[Fredoq]

Completed by #43.