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>

install.ps1

@@ -68,3 +68,10 @@ catch {
 
 Write-Host "[mosaic-install] Done."
 Write-Host "[mosaic-install] Add to PATH: `$env:USERPROFILE\.config\mosaic\bin"
+
+$soulPath = Join-Path $TargetDir "SOUL.md"
+if (-not (Test-Path $soulPath)) {
+    Write-Host ""
+    Write-Host "[mosaic-install] Set up your agent identity by running: mosaic init"
+    Write-Host "[mosaic-install] This generates SOUL.md - the universal behavioral contract for all agent sessions."
+}