fix(json-columns): skip JSON select columns with no model scan target

Requesting a JSON sub-field (e.g. jsonvalue->'product'->>'cost') that has
no matching bun scanonly field on the model made the whole read fail with
"bun: ModelX does not have column Y", since bun scans SELECT results
straight into the typed model struct.

Add reflection.HasColumn to check whether the model can actually receive
a given column (including scanonly fields, walking embedded structs), and
gate the JSON select-column expression on it in ApplySelectColumns
(shared by websocketspec/mqttspec) and the resolvespec/restheadspec
handlers. When there's no scan target, drop just that column with a
warning instead of erroring the whole request.

pkg/common/json_condition.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"strings"
 
+	"github.com/bitechdev/ResolveSpec/pkg/logger"
 	"github.com/bitechdev/ResolveSpec/pkg/reflection"
 )
 
@@ -72,6 +73,15 @@ func ResolveJSONColumnExpr(model interface{}, tableAlias, token string) (expr st
 func ApplySelectColumns(query SelectQuery, model interface{}, tableAlias string, columns []string) SelectQuery {
 	for _, col := range columns {
 		if expr, args, alias, ok := ResolveJSONColumnExpr(model, tableAlias, col); ok {
+			if !reflection.HasColumn(model, alias) {
+				// No matching scan target on the model (e.g. no
+				// `bun:"<alias>,scanonly"` field declared for this JSON
+				// path) - bun would fail to scan the row with "does not
+				// have column X". Drop the expression rather than erroring;
+				// the rest of the requested columns still get selected.
+				logger.Warn("Skipping JSON select column %q: model has no scan target for alias %q", col, alias)
+				continue
+			}
 			query = query.ColumnExpr(expr+" AS "+QuoteIdent(alias), args...)
 			continue
 		}