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/architecture.md

@@ -0,0 +1,119 @@
+# BaraDB Architecture
+
+## Overview
+
+BaraDB is a **multimodal database engine** written in Nim that combines document (KV), graph, vector, columnar, and full-text search storage in a single engine with a unified query language called **BaraQL**.
+
+## Layer Architecture
+
+```
+┌─────────────────────────────────────────────────────────┐
+│ 1. CLIENT LAYER                                          │
+│    Binary Protocol │ HTTP/REST │ WebSocket │ Embedded    │
+├─────────────────────────────────────────────────────────┤
+│ 2. QUERY LAYER (BaraQL)                                  │
+│    Lexer → Parser → AST → IR → Optimizer → Codegen      │
+├─────────────────────────────────────────────────────────┤
+│ 3. EXECUTION ENGINE                                      │
+│    Document │ Graph │ Vector │ Columnar │ FTS            │
+├─────────────────────────────────────────────────────────┤
+│ 4. STORAGE                                               │
+│    LSM-Tree │ B-Tree │ WAL │ Bloom │ Compaction │ Cache  │
+├─────────────────────────────────────────────────────────┤
+│ 5. DISTRIBUTED                                           │
+│    Raft Consensus │ Sharding │ Replication │ Gossip      │
+└─────────────────────────────────────────────────────────┘
+```
+
+## Layer 1: Client Layer
+
+Multiple communication protocols:
+
+- **Binary Protocol** (`protocol/wire.nim`): Efficient big-endian binary protocol with 16 message types
+- **HTTP/REST** (`protocol/http.nim`): JSON-based REST API
+- **WebSocket** (`protocol/websocket.nim`): Full-duplex streaming
+- **Embedded** (`storage/lsm.nim`): Direct in-process access
+
+## Layer 2: Query Layer (BaraQL)
+
+The BaraQL pipeline:
+
+1. **Lexer** (`query/lexer.nim`): Tokenizes input into 80+ token types
+2. **Parser** (`query/parser.nim`): Recursive descent parser producing AST
+3. **AST** (`query/ast.nim`): 300+ lines covering 25+ node kinds
+4. **IR** (`query/ir.nim`): Intermediate representation for execution plans
+5. **Optimizer/Codegen** (`query/codegen.nim`): Translates IR to storage operations
+
+## Layer 3: Execution Engine
+
+### Document/KV Engine
+- **LSM-Tree** (`storage/lsm.nim`): Write-optimized storage
+- **B-Tree Index** (`storage/btree.nim`): Ordered index for range scans
+
+### Vector Engine (`vector/`)
+- **HNSW Index**: Hierarchical Navigable Small World graph
+- **IVF-PQ Index**: Inverted File Index with Product Quantization
+- **SIMD Operations**: Unrolled distance computations
+
+### Graph Engine (`graph/`)
+- **Adjacency List**: Edge-weighted directed graph
+- **Algorithms**: BFS, DFS, Dijkstra, PageRank, Louvain
+
+### Full-Text Search (`fts/`)
+- **Inverted Index**: Term-document index
+- **Ranking**: BM25 and TF-IDF scoring
+- **Multi-Language**: Tokenizers for EN, BG, DE, FR, RU
+
+### Columnar Engine (`core/columnar.nim`)
+- Per-column storage for analytical queries
+- RLE and dictionary encoding
+
+## Layer 4: Storage
+
+- **LSM-Tree**: MemTable, WAL, SSTable, Bloom Filter, Compaction
+- **Page Cache**: LRU cache with hit rate tracking
+- **Memory-mapped I/O**: mmap-based file access
+
+## Layer 5: Distributed
+
+- **Raft Consensus**: Leader election, log replication
+- **Sharding**: Hash, range, and consistent hashing
+- **Replication**: Sync, async, semi-sync modes
+- **Gossip Protocol**: Membership management
+
+## Data Flow
+
+### Write Path
+```
+Client → Protocol → Auth → Parser → AST → IR → Codegen
+  → StorageOp → MVCC Txn → WAL Write → MemTable → Commit
+```
+
+### Read Path
+```
+Client → Protocol → Auth → Parser → AST → IR → Codegen
+  → StorageOp → MVCC Snapshot → MemTable → SSTable → Result
+```
+
+## Key Design Decisions
+
+1. **Pure Nim**: No Cython, Python, or Rust dependencies
+2. **Unified Storage**: One engine handles KV, graph, vector, FTS, and columnar
+3. **Embedded Mode**: Can run as library or server
+4. **Binary Protocol**: Custom efficient wire protocol
+5. **MVCC**: Multi-version concurrency control
+6. **Schema-First**: Strongly typed schema system with inheritance
+
+## Module Statistics
+
+| Category | Modules |
+|----------|---------|
+| Core | 10 |
+| Storage | 7 |
+| Query | 7 |
+| Vector | 3 |
+| Graph | 3 |
+| FTS | 2 |
+| Protocol | 7 |
+| Distributed | 5 |
+| **Total** | **48** |