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/query/executor.nim

@@ -377,6 +377,8 @@ proc validateType*(colType: string, value: string): (bool, string) =
       return (false, "Type mismatch: expected " & t & " but got '" & value & "'")
   return (true, "")
 
+proc lowerExpr*(node: Node): IRExpr
+
 proc validateConstraints*(ctx: ExecutionContext, tableName: string,
     fields: seq[string], values: seq[seq[string]]): (bool, string) =
   let tbl = ctx.getTableDef(tableName)