Add CLAUDE.md with project guidance for Claude Code

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Build and Run Commands
+
+```bash
+# Install dependencies
+uv sync
+
+# Run the application (from project root)
+./run.sh
+
+# Manual start (from backend directory)
+cd backend && uv run uvicorn app:app --reload --port 8000
+```
+
+The application serves at `http://localhost:8000` with API docs at `/docs`.
+
+## Architecture
+
+This is a RAG (Retrieval-Augmented Generation) chatbot for course materials using FastAPI, ChromaDB, and Claude.
+
+### Core Flow
+1. **Document Ingestion**: Course documents (`.txt`, `.pdf`, `.docx`) from `docs/` are processed on startup
+2. **Chunking**: Documents are split into sentence-based chunks with overlap for vector storage
+3. **Query Processing**: User queries trigger AI-driven tool use to search the vector store
+4. **Response Generation**: Claude generates responses using retrieved context
+
+### Key Components
+
+**Backend (`backend/`)**
+- `app.py` - FastAPI server with `/api/query` and `/api/courses` endpoints
+- `rag_system.py` - Main orchestrator connecting all components
+- `vector_store.py` - ChromaDB wrapper with two collections: `course_catalog` (metadata) and `course_content` (chunks)
+- `ai_generator.py` - Claude API integration with tool-use support
+- `document_processor.py` - Parses course documents and chunks text
+- `search_tools.py` - Tool interface for AI to search course content
+- `session_manager.py` - Conversation history management
+- `models.py` - Pydantic models: `Course`, `Lesson`, `CourseChunk`
+
+**Frontend (`frontend/`)** - Static HTML/CSS/JS served by FastAPI
+
+### Document Format
+Course documents follow a specific format:
+```
+Course Title: [title]
+Course Link: [url]
+Course Instructor: [instructor]
+
+Lesson 0: Introduction
+Lesson Link: [url]
+[content]
+
+Lesson 1: [title]
+...
+```
+
+### Configuration
+- `config.py` - Settings loaded from environment (`.env` file required with `ANTHROPIC_API_KEY`)
+- Default embedding model: `all-MiniLM-L6-v2`
+- Default Claude model: `claude-sonnet-4-20250514`