feat: centralized SOUL.md, mosaic-init generator, and unified launcher

- Add SOUL.md.template with {{PLACEHOLDERS}} for interactive generation
- Add mosaic-init (bash + PS1) for interactive SOUL.md creation with flag overrides
- Add mosaic launcher (bash + PS1) — unified CLI for claude/opencode/codex with SOUL.md injection
- Add codex runtime adapter (runtime/codex/instructions.md)
- Update runtime adapters (claude, opencode) with SOUL.md read directive
- Update mosaic-link-runtime-assets to push codex adapter to ~/.codex/
- Update installers to prompt for mosaic init when SOUL.md is missing

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

bin/mosaic-link-runtime-assets

@@ -86,5 +86,12 @@ if [[ -f "$opencode_adapter" ]]; then
   copy_file_managed "$opencode_adapter" "$HOME/.config/opencode/AGENTS.md"
 fi
 
+# Codex runtime adapter (optional, copied when present).
+codex_adapter="$MOSAIC_HOME/runtime/codex/instructions.md"
+if [[ -f "$codex_adapter" ]]; then
+  mkdir -p "$HOME/.codex"
+  copy_file_managed "$codex_adapter" "$HOME/.codex/instructions.md"
+fi
+
 echo "[mosaic-link] Runtime assets synced (non-symlink mode)"
 echo "[mosaic-link] Canonical source: $MOSAIC_HOME"