docs: add initial README and OpenSpec proposal

Add comprehensive README.md documenting project purpose, architecture,
tech stack, and development workflow. Includes OpenSpec proposal
(add-initial-readme) with project documentation specification.

The README describes current state only (early development phase) and
serves as entry point for developers and AI assistants.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

openspec/changes/add-initial-readme/proposal.md

@@ -0,0 +1,16 @@
+# Add Initial README
+
+## Why
+The project currently has no README.md file. According to `openspec/project.md`, we maintain a README.md as the primary project documentation and entry point for developers and AI assistants. A README is essential for anyone discovering this repository on Codeberg.
+
+## What Changes
+- Add README.md to project root describing current state
+- Document the project's purpose and vision
+- Explain OpenSpec-based development workflow
+- Provide setup instructions for contributors
+- **Note**: README describes *current* state only, not planned features
+
+## Impact
+- Affected specs: project-documentation (new capability)
+- Affected code: None (documentation only)
+- No breaking changes