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/postgres/migrations/00003_feedback_app_version.sql

@@ -0,0 +1,10 @@
+-- Capture the client app version (the build a report was sent from) with each feedback
+-- message, so the operator console can show which version a player was on. Nullable, so the
+-- rows that predate this keep working — additive and backward-compatible, so a backend image
+-- rollback stays DB-safe (older code simply ignores the column).
+
+-- +goose Up
+ALTER TABLE backend.feedback_messages ADD COLUMN app_version text;
+
+-- +goose Down
+ALTER TABLE backend.feedback_messages DROP COLUMN app_version;