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/graph.md

@@ -0,0 +1,28 @@
+# Graph Engine
+
+Съхранение със списък от съседи и вградени алгоритми.
+
+## Употреба
+
+```nim
+import barabadb/graph/engine
+
+var g = newGraph()
+let alice = g.addNode("Person", {"name": "Alice"}.toTable)
+let bob = g.addNode("Person", {"name": "Bob"}.toTable)
+discard g.addEdge(alice, bob, "knows")
+
+let bfs = g.bfs(alice)
+let path = g.shortestPath(alice, bob)
+let ranks = g.pageRank()
+```
+
+## Алгоритми
+
+| Алгоритъм | Описание |
+|-----------|----------|
+| `bfs` | breadth-first обхождане |
+| `dfs` | depth-first обхождане |
+| `dijkstra` | Най-кратък път с тегла |
+| `pageRank` | Ранг на възел |
+| `louvain` | Откриване на общности |