feat(feedback): capture the app version; show version + local Filed time

Each feedback submission now carries the client app version (__APP_VERSION__),
snapshotted like the interface language: FlatBuffers FeedbackSubmitRequest gains
a version field → gateway transcode → backend, persisted in a new nullable
feedback_messages.app_version column (migration 00003, additive so an image
rollback stays DB-safe). The operator console detail shows the app version and
renders the Filed time in UTC plus the sender's time zone (fmtTimeIn).

Touches: fbs schema + regenerated Go/TS codegen, codec + transport (the client
attaches its build), gateway transcode + backendclient, feedback store/service,
admin view + template, docs (ARCHITECTURE §15, FUNCTIONAL + _ru). Verified:
feedback integration tests (migration + version round-trip), codec round-trip,
check/unit/build green.

backend/internal/server/handlers_feedback.go

@@ -16,6 +16,9 @@ type feedbackSubmitRequest struct {
 	Attachment     string `json:"attachment"`
 	AttachmentName string `json:"attachment_name"`
 	Channel        string `json:"channel"`
+	// Version is the client's app version (pkg/version / the SPA build), snapshotted so the
+	// operator sees which build a report came from.
+	Version string `json:"version"`
 }
 
 // feedbackReplyDTO is the operator's reply shown back to the player.
@@ -61,7 +64,7 @@ func (s *Server) handleFeedbackSubmit(c *gin.Context) {
 		}
 		attachment = data
 	}
-	if err := s.feedback.Submit(c.Request.Context(), uid, req.Body, attachment, req.AttachmentName, req.Channel, clientIP(c)); err != nil {
+	if err := s.feedback.Submit(c.Request.Context(), uid, req.Body, attachment, req.AttachmentName, req.Channel, req.Version, clientIP(c)); err != nil {
 		s.abortErr(c, err)
 		return
 	}