[TSC-15] Add CLAUDE.md for docs repository

Documents repository purpose, structure, and conventions for the
test-simple-calculator-docs AI-SDLC artifacts repo.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -0,0 +1,40 @@
+# CLAUDE.md
+
+## Project Overview
+
+This is a documentation-only repository containing AI-SDLC artifacts (approved spec and Technical Architecture Document) for the **Test Simple Calculator** project. There is no application code, build system, or test suite.
+
+## Build Commands
+
+No build system. This repository contains only Markdown documentation files.
+
+## Test Commands
+
+No automated tests. Review documents manually for correctness.
+
+## Development Commands
+
+No dev server. Open `.md` files directly in any Markdown viewer or editor.
+
+## Project Structure
+
+```
+.
+├── README.md   — Repository description
+└── CLAUDE.md   — This file
+```
+
+Additional documentation files (spec, TAD) may be added at the repository root or in subdirectories as the project evolves.
+
+## Architecture Notes
+
+- **AI-SDLC docs repo**: Stores approved specification and Technical Architecture Document for the Test Simple Calculator project.
+- No application code lives here; this repository is purely for design and planning artifacts.
+- Documents should be kept in Markdown format for portability and version control compatibility.
+
+## Code Style
+
+No code is present. For documentation:
+- Use standard GitHub-Flavored Markdown.
+- Keep line lengths reasonable (~120 characters) for readability in diffs.
+- Use ATX-style headers (`#`, `##`, etc.).