fix: remove --append-system-prompt-file from launcher

SOUL.md injection happens via ~/.claude/CLAUDE.md directive (pushed by
mosaic-link-runtime-assets), not CLI flags. The launcher now just does
pre-flight checks and launches the runtime directly.

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

bin/mosaic.ps1

@@ -73,9 +73,9 @@ switch ($command) {
         Assert-MosaicHome
         Assert-Soul
         Assert-Runtime "claude"
-        $soulFile = Join-Path $MosaicHome "SOUL.md"
-        Write-Host "[mosaic] Launching Claude Code with SOUL.md injection..."
-        & claude --append-system-prompt-file $soulFile @remaining
+        # SOUL.md is loaded via ~/.claude/CLAUDE.md directive (pushed by mosaic-link-runtime-assets)
+        Write-Host "[mosaic] Launching Claude Code..."
+        & claude @remaining
     }
     "opencode" {
         Assert-MosaicHome