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/distributed.md

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+# Distributed Systems
+
+BaraDB supports distributed deployment with Raft consensus, sharding, and replication.
+
+## Raft Consensus
+
+Leader election and log replication:
+
+```nim
+import barabadb/core/raft
+
+var cluster = newRaftCluster()
+cluster.addNode("node1")
+cluster.addNode("node2")
+cluster.addNode("node3")
+
+let n1 = cluster.nodes["n1"]
+n1.becomeCandidate()
+n1.becomeLeader()
+let entry = n1.appendLog("SET key1 value1")
+```
+
+## Sharding
+
+Distribute data across nodes:
+
+```nim
+import barabadb/core/sharding
+
+var router = newShardRouter(ShardConfig(
+  numShards: 4,
+  replicas: 2,
+  strategy: ssHash
+))
+router.rebalance(@["node1", "node2", "node3"])
+let shard = router.getShard("user_123")
+```
+
+### Sharding Strategies
+
+| Strategy | Description |
+|----------|-------------|
+| `ssHash` | Hash-based sharding |
+| `ssRange` | Range-based sharding |
+| `ssConsistent` | Consistent hashing |
+
+## Replication
+
+```nim
+import barabadb/core/replication
+
+var rm = newReplicationManager(rmSync)
+rm.addReplica(newReplica("r1", "10.0.0.1", 5432))
+rm.connectReplica("r1")
+let lsn = rm.writeLsn(@[1'u8, 2, 3])
+rm.ackLsn("r1", lsn)
+```
+
+### Replication Modes
+
+| Mode | Description |
+|------|-------------|
+| `rmSync` | Synchronous replication |
+| `rmAsync` | Asynchronous replication |
+| `rmSemiSync` | Semi-synchronous replication |
+
+## Gossip Protocol
+
+Membership and failure detection:
+
+```nim
+import barabadb/core/gossip
+
+var g = newGossipManager()
+g.addNode("node1")
+g.addNode("node2")
+g.tick()  # Exchange membership info
+```
+
+## Distributed Transactions
+
+Two-phase commit across nodes:
+
+```nim
+import barabadb/core/disttxn
+
+var dt = newDistributedTxn()
+dt.prepare(@["node1", "node2"])
+dt.commit()
+```