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.

CHANGELOG.md

@@ -8,11 +8,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added
+- Init wizard with daemon install step (`unarr init`, replaces `unarr setup`)
+- Interactive config menu with 7 categories (`unarr config [category]`)
 - Clean command to remove temp files, logs, and cached data (`unarr clean`)
 - Daemon mode with background download management (`unarr start`)
 - One-shot download command (`unarr download`)
 - Stream to media player (`unarr stream`)
-- Setup wizard for first-time configuration (`unarr setup`)
 - Doctor command for diagnostics (`unarr doctor`)
 - Status command for daemon monitoring (`unarr status`)
 - Download engine with torrent support (debrid and usenet coming soon)