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/storage.md

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+# Storage Engines
+
+BaraDB provides multiple storage engines optimized for different access patterns.
+
+## LSM-Tree (Key-Value)
+
+The primary storage engine with write-optimized append-only log structure.
+
+### Usage
+
+```nim
+import barabadb/storage/lsm
+
+var db = newLSMTree("./data")
+db.put("key1", cast[seq[byte]]("value1"))
+let (found, value) = db.get("key1")
+db.close()
+```
+
+### Components
+
+- **MemTable**: In-memory sorted buffer
+- **WAL**: Write-ahead log for durability
+- **SSTable**: Sorted string tables on disk
+- **Bloom Filter**: Probabilistic set membership
+- **Compaction**: Size-tiered strategy with level management
+- **Page Cache**: LRU cache with hit rate tracking
+
+## B-Tree Index
+
+Ordered index for range scans and point lookups.
+
+### Usage
+
+```nim
+import barabadb/storage/btree
+
+var btree = newBTreeIndex[string, string]()
+btree.insert("key1", "value1")
+let values = btree.get("key1")
+let range = btree.scan("key_a", "key_z")
+```
+
+## Write-Ahead Log (WAL)
+
+Ensures durability of write operations.
+
+```nim
+import barabadb/storage/wal
+
+var wal = newWAL("./wal")
+wal.append("txn1", "SET key1 value1")
+wal.flush()
+```
+
+## Bloom Filter
+
+Probabilistic data structure for fast negative lookups.
+
+```nim
+import barabadb/storage/bloom
+
+var filter = newBloomFilter(10000, 0.01)
+filter.add("key1")
+if filter.mightContain("key1"):
+  echo "possibly exists"
+```
+
+## Memory-mapped I/O
+
+Efficient file access using mmap.
+
+```nim
+import barabadb/storage/mmap
+
+var mapped = mmapFile("./data/file.dat")
+let data = mapped.read(0, 100)
+```