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/lsm.md

@@ -0,0 +1,64 @@
+# LSM-Tree Storage Engine
+
+The primary storage engine in BaraDB using the Log-Structured Merge-Tree architecture.
+
+## Architecture
+
+```
+┌─────────────────────────────────────────────┐
+│                   Writes                     │
+│         (append to WAL + MemTable)           │
+└─────────────────────────────────────────────┘
+                      │
+                      ▼
+┌─────────────────────────────────────────────┐
+│                  MemTable                    │
+│         (in-memory sorted buffer)            │
+└─────────────────────────────────────────────┘
+                      │
+           (when full, flush to SSTable)
+                      │
+                      ▼
+┌─────────────────────────────────────────────┐
+│                  SSTable                     │
+│          (sorted string table on disk)       │
+└─────────────────────────────────────────────┘
+```
+
+## Usage
+
+```nim
+import barabadb/storage/lsm
+
+var db = newLSMTree("./data")
+
+# Write
+db.put("key1", cast[seq[byte]]("value1"))
+
+# Read
+let (found, value) = db.get("key1")
+
+# Delete
+db.delete("key1")
+
+db.close()
+```
+
+## Features
+
+- **Write-optimized**: Append-only log structure
+- **Durability**: Write-ahead log (WAL) ensures crash recovery
+- **Bloom Filter**: Fast negative lookups
+- **Compaction**: Size-tiered strategy merges SSTables
+- **Page Cache**: LRU cache for frequently accessed pages
+
+## Configuration
+
+```nim
+var db = newLSMTree(
+  path = "./data",
+  memTableSize = 64 * 1024 * 1024,  # 64MB
+  walEnabled = true,
+  bloomFpRate = 0.01
+)
+```