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/en/columnar.md

@@ -0,0 +1,58 @@
+# Columnar Storage
+
+Column-oriented storage for analytical queries and aggregations.
+
+## Usage
+
+```nim
+import barabadb/core/columnar
+
+var batch = newColumnBatch()
+var ageCol = batch.addInt64Col("age")
+var nameCol = batch.addStringCol("name")
+
+ageCol.appendInt64(25)
+nameCol.appendString("Alice")
+```
+
+## Aggregations
+
+```nim
+echo ageCol.sumInt64()
+echo ageCol.avgInt64()
+echo ageCol.minInt64()
+echo ageCol.maxInt64()
+echo ageCol.count()
+```
+
+## Encoding
+
+### RLE (Run-Length Encoding)
+
+```nim
+let rle = rleEncode(@[1'i64, 1, 1, 2, 2, 3])
+```
+
+### Dictionary Encoding
+
+```nim
+let dict = dictEncode(@["apple", "banana", "apple"])
+```
+
+## Column Types
+
+| Type | Description |
+|------|-------------|
+| `int32` | 32-bit integer |
+| `int64` | 64-bit integer |
+| `float32` | 32-bit float |
+| `float64` | 64-bit float |
+| `string` | Variable-length string |
+| `bool` | Boolean |
+
+## Use Cases
+
+- OLAP workloads
+- Large-scale aggregations
+- Data warehousing
+- Time-series analysis