docs: add project purpose and principles to .claude.md

Author: williamfiset

.claude.md

@@ -2,6 +2,16 @@
 
 This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
 
+## Project Purpose
+
+This is an **educational algorithms and data structures repository**. The core goal is to provide clear, well-tested, and accessible implementations for learners who may not have deep computer science backgrounds.
+
+**Key Principles:**
+- **Every file should teach**, not just implement.
+- Implementations should be simple, elegant, and avoid unnecessary complexity (e.g., prefer plain loops over Java Streams).
+- Documentation must explain *how* and *why* an algorithm works, including time and space complexity.
+- Every algorithm must be accompanied by comprehensive tests that cover edge cases and teach through examples.
+
 ## Build System
 
 This project uses **Bazel** as its build system (requires JDK 8+). Dependencies are managed via Maven through `rules_jvm_external` and declared in `MODULE.bazel`.