spec: harness-sync v1 design

Canonical config at ~/.config/harness-sync/ (git repo) propagates skills,
agents, MCP, LLM endpoints (via profiles), and global instructions into
each detected harness. Hybrid sync: symlinks where shapes match, rendered
files where they differ. Plugin-style adapters; conflict resolution via
git merge-file three-way merge tracked in state/.

.gitignore

@@ -0,0 +1,16 @@
+# build artifacts
+/harness-sync
+/dist/
+*.test
+*.out
+
+# go
+/vendor/
+
+# editor
+.idea/
+.vscode/
+*.swp
+
+# os
+.DS_Store