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/bg/vector.md

@@ -0,0 +1,41 @@
+# Vector Търсене
+
+HNSW и IVF-PQ индекси за търсене на прилика.
+
+## Употреба
+
+```nim
+import barabadb/vector/engine
+
+var idx = newHNSWIndex(dimensions = 128)
+idx.insert(1, @[1.0'f32, 0.0'f32, ...], {"category": "A"}.toTable)
+
+let results = idx.search(queryVector, k = 10)
+```
+
+## Индекс Типове
+
+### HNSW
+
+Иерархичен навигируем малък свят:
+
+```nim
+var hnsw = newHNSWIndex(dimensions = 128, m = 16)
+```
+
+### IVF-PQ
+
+Инвертиран файл с продуктово квантуване:
+
+```nim
+var ivfpq = newIVFPQIndex(dimensions = 128, numCentroids = 256)
+```
+
+## Метрики за Разстояние
+
+| Метрика | Описание |
+|---------|----------|
+| `cosine` | Косинусова прилика |
+| `euclidean` | L2 разстояние |
+| `dotproduct` | Скаларно произведение |
+| `manhattan` | L1 разстояние |