fix(admin): keep the filter query intact in console pager and export links

The paginated users and messages lists interpolate the pre-encoded filter
query (url.Values.Encode) after the "?" in their pager and CSV-export links.
There html/template treats it as a single query value and percent-encodes the
structural "=" and "&" again, so "kind=robots" rendered as "kind%3drobots" and
the multi-pair message filter collapsed -- every page step dropped the active
filter.

Type FilterQuery as template.URL so the already-escaped fragment is emitted
verbatim (the attribute-level "&" -> "&" stays correct, the browser decodes
it back). It is safe because url.Values.Encode output is strictly
percent-encoded. games/complaints use status={{.Status}} -- a single value in
proper query-value context -- and were never affected.

backend/internal/server/handlers_admin_console.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/csv"
 	"fmt"
+	"html/template"
 	"net/http"
 	"net/url"
 	"path/filepath"
@@ -108,7 +109,7 @@ func (s *Server) consoleUsers(c *gin.Context) {
 	view := adminconsole.UsersView{
 		Pager:  adminconsole.NewPager(page, adminPageSize, total),
 		Robots: filter.Robots, NameMask: filter.NameMask, ExternalIDMask: filter.ExternalIDMask,
-		FilterQuery: q.Encode(),
+		FilterQuery: template.URL(q.Encode()),
 	}
 	ids := make([]uuid.UUID, 0, len(items))
 	for _, it := range items {
@@ -174,7 +175,7 @@ func (s *Server) consoleMessages(c *gin.Context) {
 		Pager:       adminconsole.NewPager(page, adminPageSize, total),
 		NameMask:    filter.NameMask,
 		ExtMask:     filter.ExtMask,
-		FilterQuery: q.Encode(),
+		FilterQuery: template.URL(q.Encode()),
 	}
 	if filter.GameID != uuid.Nil {
 		view.GameID = filter.GameID.String()