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.

ui/src/lib/codec.test.ts

@@ -76,18 +76,20 @@ describe('codec', () => {
   it('round-trips a feedback submit and decodes state + unread', () => {
     const att = new Uint8Array([1, 2, 3, 4]);
     const req = fb.FeedbackSubmitRequest.getRootAsFeedbackSubmitRequest(
-      new ByteBuffer(encodeFeedbackSubmit('please fix', att, 'shot.png', 'ios')),
+      new ByteBuffer(encodeFeedbackSubmit('please fix', att, 'shot.png', 'ios', 'v1.2.3')),
     );
     expect(req.body()).toBe('please fix');
     expect(req.attachmentName()).toBe('shot.png');
     expect(req.channel()).toBe('ios');
+    expect(req.version()).toBe('v1.2.3');
     expect(Array.from(req.attachmentArray() ?? [])).toEqual([1, 2, 3, 4]);
 
     // No attachment: the vector is empty.
     const req2 = fb.FeedbackSubmitRequest.getRootAsFeedbackSubmitRequest(
-      new ByteBuffer(encodeFeedbackSubmit('hi', null, '', 'web')),
+      new ByteBuffer(encodeFeedbackSubmit('hi', null, '', 'web', 'dev')),
     );
     expect(req2.body()).toBe('hi');
+    expect(req2.version()).toBe('dev');
     expect(req2.attachmentLength()).toBe(0);
 
     // State carrying a reply.