feat: add universal skill sync and runtime linking

README.md

@@ -16,6 +16,36 @@ bash ~/src/mosaic-bootstrap/install.sh
 - Shared standards document: `~/.mosaic/STANDARDS.md`
 - Runtime adapter docs: `~/.mosaic/adapters/`
 - Shared wrapper commands: `~/.mosaic/bin/`
+- Canonical skills directory: `~/.mosaic/skills`
+
+## Universal Skills
+
+The installer syncs skills from:
+
+- `https://git.mosaicstack.dev/mosaic/agent-skills`
+
+into:
+
+- `~/.mosaic/skills`
+
+Then links each skill into runtime directories:
+
+- `~/.claude/skills`
+- `~/.codex/skills`
+- `~/.config/opencode/skills`
+
+Manual commands:
+
+```bash
+~/.mosaic/bin/mosaic-sync-skills
+~/.mosaic/bin/mosaic-sync-skills --link-only
+```
+
+Opt-out during install:
+
+```bash
+MOSAIC_SKIP_SKILLS_SYNC=1 bash ~/src/mosaic-bootstrap/install.sh
+```
 
 ## Usage