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.

install.ps1

@@ -153,7 +153,7 @@ function Install-Docker {
     Write-Host "  mkdir `$env:APPDATA\unarr"
     Write-Host ""
     Write-Host "  # 2. Run setup (interactive)"
-    Write-Host "  docker run -it --rm -v `$env:APPDATA\unarr:/config torrentclaw/unarr setup"
+    Write-Host "  docker run -it --rm -v `$env:APPDATA\unarr:/config torrentclaw/unarr init"
     Write-Host ""
     Write-Host "  # 3. Start daemon"
     Write-Host "  docker run -d --name unarr --restart unless-stopped ``"
@@ -238,7 +238,7 @@ function Main {
             Install-Binary
             Write-Host ""
             Write-Host "  Run " -NoNewline
-            Write-Host "unarr setup" -ForegroundColor White -NoNewline
+            Write-Host "unarr init" -ForegroundColor White -NoNewline
             Write-Host " to get started."
             Write-Host ""
         }