Add comprehensive documentation with i18n support (EN/BG)

- Add docs/ folder with English (en/) and Bulgarian (bg/) documentation
- Create index.md with language switching and links
- English docs: installation, quickstart, architecture, baraql, storage,
  schema, lsm, btree, vector, graph, fts, columnar, transactions,
  distributed, protocol, udf, api-binary, api-http, api-websocket
- Bulgarian docs: installation, quickstart, architecture, baraql,
  schema, lsm, btree, vector, graph, fts, transactions, distributed
- Update README license to BSD 3-Clause
- Add LICENSE file with BSD 3-Clause text

docs/index.md

@@ -0,0 +1,53 @@
+# BaraDB Documentation
+
+**A multimodal database engine written in Nim — 100% native, zero dependencies.**
+
+## Documentation Languages
+
+- [English](en/)
+- [Български (Bulgarian)](bg/)
+
+---
+
+## Quick Links
+
+### Getting Started
+- [Installation](en/installation.md)
+- [Quick Start](en/quickstart.md)
+- [Architecture Overview](en/architecture.md)
+
+### Core Concepts
+- [BaraQL Query Language](en/baraql.md)
+- [Storage Engines](en/storage.md)
+- [Schema System](en/schema.md)
+
+### Engines
+- [LSM-Tree Storage](en/lsm.md)
+- [B-Tree Index](en/btree.md)
+- [Vector Search](en/vector.md)
+- [Graph Engine](en/graph.md)
+- [Full-Text Search](en/fts.md)
+- [Columnar Storage](en/columnar.md)
+
+### Advanced
+- [Transactions & MVCC](en/transactions.md)
+- [Distributed Systems](en/distributed.md)
+- [Protocol Reference](en/protocol.md)
+- [User Defined Functions](en/udf.md)
+
+### API Reference
+- [Binary Protocol](en/api-binary.md)
+- [HTTP/REST API](en/api-http.md)
+- [WebSocket API](en/api-websocket.md)
+
+---
+
+## Project Info
+
+- [Contributing](../CONTRIBUTING.md)
+- [License](../LICENSE)
+- [GitHub Repository](https://github.com/katehonz/barabaDB)
+
+---
+
+*To add a new language, create a new folder in `docs/` with the language code (e.g., `docs/de/`) and add a link above.*