Initial commit: add .gitignore and README

decisions/0003-use-git-submodules.md

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+# ADR-0003: Use Git Submodules for External Projects
+
+**Status**: Accepted
+**Date**: 2025-01-27
+**Deciders**: Workspace maintainers
+
+---
+
+## Context
+
+We need to include external projects or existing repositories in monorepos. Options include:
+- Git submodules
+- Copying code into monorepo
+- Converting to workspace packages
+
+---
+
+## Decision
+
+We will use Git submodules for:
+- External repositories
+- Existing projects that should maintain independent versioning
+- Projects maintained separately
+
+We will use workspace packages for:
+- New shared code
+- Internal libraries
+- Code that benefits from unified versioning
+
+---
+
+## Consequences
+
+### Positive
+- ✅ Maintains repository independence
+- ✅ Allows independent versioning
+- ✅ Preserves git history
+- ✅ Easier external contribution
+
+### Negative
+- ⚠️ Submodule complexity
+- ⚠️ Requires submodule management knowledge
+- ⚠️ Can complicate workflow
+
+---
+
+**Status**: Accepted
+