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>

runtime/codex/instructions.md

@@ -0,0 +1,19 @@
+# Mosaic Runtime Adapter — Codex
+
+## MANDATORY — Read Before Any Response
+
+BEFORE responding to any user message, READ these files in order:
+
+1. `~/.config/mosaic/SOUL.md` (identity and behavioral contract)
+2. `~/.config/mosaic/STANDARDS.md` (machine-wide standards)
+3. Project-local `AGENTS.md` (project operations and workflows)
+
+Do NOT respond to the user until you have loaded all three.
+
+This file is a Codex adapter layer. It does not replace project guidance.
+
+## Runtime Behavior
+
+- Favor repo lifecycle scripts under `scripts/agent/` for start/end rituals.
+- Keep instructions and quality gates aligned with Mosaic standards.
+- Use `~/.config/mosaic/skills/` for domain expertise when available.