feat: replace setup with init wizard + interactive config menu
- `unarr init` (alias: `unarr setup`): streamlined 3-step wizard
(API key, download dir, daemon install). Removed method/name prompts
— auto-configured from defaults.
- `unarr config [category]`: interactive menu with 7 categories
(downloads, organization, notifications, device, region, connection,
advanced). Direct access via `unarr config downloads`, etc.
- Extract shared helpers (openBrowser, expandHome, isTerminal) to
helpers.go. Delete old setup.go and config.go.
- Update all "unarr setup" references to "unarr init" across daemon,
doctor, status, README, install scripts.
0b6c6849b1