feat: HTTP server in main entry point + background compaction scheduling

- baradadb.nim now starts both TCP wire protocol and HTTP REST servers
- HTTP server runs in background thread via hunos on port TCP+440
- WebSocket server auto-starts on HTTP port + 1
- CompactionManager with background async loop (default 60s interval)
- CompactionStrategy wired to LSMTree SSTables
- Fixed forward declaration for lowerExpr in executor.nim
- 216 tests passing

src/barabadb/core/httpserver.nim

@@ -8,6 +8,7 @@ import tables
 import strutils
 import os
 import times
+import std/asyncdispatch
 import config
 import ../query/lexer
 import ../query/parser
@@ -22,7 +23,7 @@ type
   HttpServer* = ref object
     config: BaraConfig
     running: bool
-    db: LSMTree
+    db*: LSMTree
     ctx: ExecutionContext
     metrics*: Metrics
     secretKey*: string