Browser import: Arc, Brave, Edge as named importers

[spaceshipmike]

Summary

Formalize Arc, Brave, and Edge as named browser importers in the CLI and dashboard. The Chrome connector already detects some Chromium paths, but these should be first-class named options.

Experience

• km import arc, km import brave, km import edge as CLI commands
• Dashboard connector setup shows each browser by name
• Auto-locates bookmark file per browser

Spec reference

.fctry/spec.md Section 2.5 — Browser import expansion