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_admin_console.go

@@ -1198,6 +1198,19 @@ func fmtTime(t time.Time) string {
 	return t.UTC().Format("2006-01-02 15:04")
 }
 
+// fmtTimeIn formats a timestamp in the named IANA zone (falling back to UTC when the zone is
+// empty or unknown), or "" when zero — for showing a time in a user's local zone beside UTC.
+func fmtTimeIn(t time.Time, tz string) string {
+	if t.IsZero() {
+		return ""
+	}
+	loc, err := time.LoadLocation(tz)
+	if err != nil {
+		loc = time.UTC
+	}
+	return t.In(loc).Format("2006-01-02 15:04")
+}
+
 // fmtTimePtr formats an optional timestamp for display, or "" when nil.
 func fmtTimePtr(t *time.Time) string {
 	if t == nil {