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/claude/CLAUDE.md

@@ -1,8 +1,14 @@
 # Mosaic Universal Standards (Machine-Wide)
 
-Before applying any runtime-specific guidance in this file, load and apply:
-- `~/.config/mosaic/STANDARDS.md`
-- project-local `AGENTS.md`
+## 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.
 
 `~/.config/mosaic` is the canonical cross-agent standards layer. This `CLAUDE.md` is an adapter layer for Claude-specific capabilities only.