docs: consolidate and clean up documentation

- Remove redundant files: AGENTS.md, INSTRUCTIONS.yaml, instructions.mdc
- Create comprehensive CONTRIBUTING.md with all development guidelines
- Add simple documentation index at docs/README.md
- Update main README to reference consolidated docs
- Remove implementation notes and release summaries
- Keep only essential, current documentation

.github/copilot-instructions.md

@@ -0,0 +1,50 @@
+Here’s a clean **developer guide in Markdown** format, ready to drop into your repo as `INSTRUCTIONS.md`. It captures your constraints, rules, and workflows in a human-readable but precise style.
+
+---
+
+# Development Instructions
+
+## Project Context
+
+* **UnitForge** is in **development**.
+* The project is **not in production**.
+* **No compatibility requirements** between major code changes.
+* Guiding principle: **Keep it small and simple**.
+
+## Development Rules
+
+1. **Fix lint errors** – Code must always pass lint checks.
+2. **Keep code lean** – Avoid unnecessary abstractions; keep it direct.
+3. **Keep tests consistent** – All tests must pass; write tests for new code.
+4. **Remove legacy code** – Delete or refactor outdated code.
+5. **Use Makefile for services** – Prefer `make` targets to run and manage services.
+6. **Server** – Run the backend with **Uvicorn**.
+7. **Package management** – Use **uv** exclusively, never pip.
+
+## Common Commands
+
+| Task                 | Command                    |
+| -------------------- | -------------------------- |
+| Setup environment    | `make setup-dev`           |
+| Run server           | `make server`              |
+| Run tests            | `make test`                |
+| Run tests (coverage) | `make test-cov`            |
+| Lint & format code   | `make lint && make format` |
+| Full dev cycle       | `make dev`                 |
+
+## Style Guidelines
+
+* **Python**:
+
+  * Follow **PEP 8**.
+  * Use **type hints** consistently.
+  * Format code with **Black**.
+* **Code quality**:
+
+  * Avoid duplication.
+  * Keep modules cohesive.
+  * Minimize complexity.
+
+---
+
+Would you like me to also add a **“Workflow Examples”** section (e.g. *how to add a new feature step-by-step*) to make onboarding even smoother for future contributors?