fix: installer auto-adds mosaic bin to PATH with clear status output

- install.sh: detects shell profile (zsh/bash/profile), adds PATH entry if missing
- install.ps1: adds to User PATH via SetEnvironmentVariable if missing
- Both are idempotent — show "already in PATH ✓" on re-run
- mosaic/mosaic.ps1: accept "help" and "version" as bare subcommands

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

bin/mosaic.ps1

@@ -108,8 +108,8 @@ switch ($command) {
         Write-Host "[mosaic] NOTE: mosaic-bootstrap-repo requires bash. Use Git Bash or WSL." -ForegroundColor Yellow
         & (Join-Path $MosaicHome "bin\mosaic-bootstrap-repo") @remaining
     }
-    { $_ -in "-h", "--help" } { Show-Usage }
-    { $_ -in "-v", "--version" } { Write-Host "mosaic $Version" }
+    { $_ -in "help", "-h", "--help" } { Show-Usage }
+    { $_ -in "version", "-v", "--version" } { Write-Host "mosaic $Version" }
     default {
         Write-Host "[mosaic] Unknown command: $command" -ForegroundColor Red
         Write-Host "[mosaic] Run 'mosaic --help' for usage."