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

@@ -71,9 +71,9 @@ launch_claude() {
   check_soul
   check_runtime "claude"
 
-  local soul_file="$MOSAIC_HOME/SOUL.md"
-  echo "[mosaic] Launching Claude Code with SOUL.md injection..."
-  exec claude --append-system-prompt-file "$soul_file" "$@"
+  # SOUL.md is loaded via ~/.claude/CLAUDE.md directive (pushed by mosaic-link-runtime-assets)
+  echo "[mosaic] Launching Claude Code..."
+  exec claude "$@"
 }
 
 launch_opencode() {