feat: initial BaraDB — multimodal database engine in Nim

- LSM-Tree storage engine with WAL, bloom filter, MemTable
- BaraQL query language: lexer (80+ tokens), recursive descent parser, AST
- Vector engine: HNSW + IVF-PQ indexes, 4 distance metrics
- Graph engine: adjacency list, BFS/DFS, Dijkstra, PageRank
- Full-Text Search: inverted index, BM25 ranking, stemming, stop words
- Type system: 17 types (int/float/string/uuid/json/vector/...)
- Async TCP server
- 21 passing tests

src/barabadb/core/server.nim

@@ -0,0 +1,48 @@
+## BaraDB Server — async TCP server
+import std/asyncdispatch
+import std/asyncnet
+import std/strutils
+import config
+
+type
+  Server* = ref object
+    config: BaraConfig
+    running: bool
+
+  ClientConnection = ref object
+    socket: AsyncSocket
+    id: int
+
+proc newServer*(config: BaraConfig): Server =
+  Server(config: config, running: false)
+
+proc handleClient(server: Server, client: AsyncSocket, clientId: int) {.async.} =
+  echo "Client ", clientId, " connected"
+  try:
+    while true:
+      let line = await client.recvLine()
+      if line.len == 0:
+        break
+      echo "[", clientId, "] ", line
+      await client.send("OK\n")
+  except:
+    discard
+  finally:
+    echo "Client ", clientId, " disconnected"
+    client.close()
+
+proc run*(server: Server) {.async.} =
+  server.running = true
+  var clientId = 0
+  let sock = newAsyncSocket()
+  sock.setSockOpt(OptReuseAddr, true)
+  sock.bindAddr(Port(server.config.port), server.config.address)
+  sock.listen()
+  echo "BaraDB listening on ", server.config.address, ":", server.config.port
+  while server.running:
+    let client = await sock.accept()
+    inc clientId
+    asyncCheck server.handleClient(client, clientId)
+
+proc stop*(server: Server) =
+  server.running = false