fix(startup): hide the FMX taskbar proxy the instant it is created

The instrumented run pinned it down: the FORM is never visible
(form_visible_was=False at all four hide points). What shows is the FMX
taskbar proxy — app=0 at 20.145, app=854682 at 20.974 — so it is created
partway through FormCreate and stayed on screen for the best part of a second
until the first hide that could see it.

A WinEvent hook on EVENT_OBJECT_SHOW, active only for the --tray startup,
hides any top-level window of ours the moment Windows shows it, and is torn
down once MinimizeToTray has run.

Two details that would each have broken it:
- WINEVENT_INCONTEXT, not OUTOFCONTEXT: the latter queues the callback until
  the thread pumps messages, which does not happen during FormCreate — exactly
  when the proxy appears.
- The pending flag is a unit-level var, not a form field: CreateForm assigns
  the MainForm global only after the constructor returns, so a callback firing
  during FormCreate could not have reached the form.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

delphi-backend/UMainForm.pas

@@ -84,6 +84,11 @@ type
     // restore's resize is indistinguishable from a user gesture by placement
     // flags or foreground ownership — both were measured and rejected).
     FWinEventHook: THandle;
+    // --tray only: catches EVENT_OBJECT_SHOW so any top-level window of ours
+    // is hidden the instant Windows shows it. The FMX taskbar proxy is created
+    // partway through FormCreate — it does not exist at the first hide points
+    // and was therefore visible for the best part of a second.
+    FShowEventHook: THandle;
     // True from "minimise starts" until just after the restore settles, so the
     // resizes FMX fires while restoring are not recorded as user intent.
     FIgnoreResizes: Boolean;
@@ -195,6 +200,11 @@ function MaskAccessToken(const AUrl: string): string; forward;
 
 // ---- WinEvent hook plumbing (see the maximised-state block further down) --
 const
+  EVENT_OBJECT_SHOW          = $8002;
+  // Synchronous delivery, in our own process. OUTOFCONTEXT would queue the
+  // callback until the thread pumps messages — which does not happen during
+  // FormCreate, exactly when we need to react.
+  WINEVENT_INCONTEXT         = $0004;
   EVENT_SYSTEM_MINIMIZESTART = $0016;
   EVENT_SYSTEM_MINIMIZEEND   = $0017;
   WINEVENT_OUTOFCONTEXT      = $0000;
@@ -207,8 +217,16 @@ function UnhookWinEvent(hWinEventHook: THandle): BOOL;
   stdcall; external 'user32.dll' name 'UnhookWinEvent';
 
 // Defined lower down, next to the window-state logic it serves.
+// Unit-level, NOT a form field: Application.CreateForm only assigns MainForm
+// after the constructor returns, so during FormCreate the global is still nil
+// and the callback could not reach the form at all.
+var
+  GTrayStartupPending: Boolean = False;
+
 procedure WinStateEventProc(hWinEventHook: THandle; AEvent: DWORD; AWnd: HWND;
   idObject, idChild: LongInt; idEventThread, dwmsEventTime: DWORD); stdcall; forward;
+procedure TrayShowEventProc(hWinEventHook: THandle; AEvent: DWORD; AWnd: HWND;
+  idObject, idChild: LongInt; idEventThread, dwmsEventTime: DWORD); stdcall; forward;
 
 procedure TMainForm.FormCreate(Sender: TObject);
 begin
@@ -223,7 +241,12 @@ begin
   begin
     Visible    := False;
     OnActivate := TrayStartupHideOnce;
-    LogLine('[tray] FormCreate begin at ' + FormatDateTime('hh:nn:ss.zzz', Now));
+    GTrayStartupPending := True;
+    FShowEventHook := SetWinEventHook(
+      EVENT_OBJECT_SHOW, EVENT_OBJECT_SHOW, 0,
+      @TrayShowEventProc, GetCurrentProcessId, 0, WINEVENT_INCONTEXT);
+    LogLine('[tray] FormCreate begin at ' + FormatDateTime('hh:nn:ss.zzz', Now) +
+            ' show-hook=' + BoolToStr(FShowEventHook <> 0, True));
     TrayHideNow('hide#1 top-of-FormCreate');
   end;
 
@@ -338,6 +361,12 @@ begin
       procedure
       begin
         FBridge.MinimizeToTray;
+        GTrayStartupPending := False;
+        if FShowEventHook <> 0 then
+        begin
+          UnhookWinEvent(FShowEventHook);
+          FShowEventHook := 0;
+        end;
         LogLine('[tray] deferred MinimizeToTray ran at ' +
                 FormatDateTime('hh:nn:ss.zzz', Now));
       end);
@@ -351,6 +380,11 @@ begin
     UnhookWinEvent(FWinEventHook);
     FWinEventHook := 0;
   end;
+  if FShowEventHook <> 0 then
+  begin
+    UnhookWinEvent(FShowEventHook);
+    FShowEventHook := 0;
+  end;
   if Assigned(FFileSaveChunks) then
   begin
     for var LSB in FFileSaveChunks.Values do LSB.Free;
@@ -1608,6 +1642,19 @@ begin
   else if AEvent = EVENT_SYSTEM_MINIMIZEEND then MainForm.WinStateMinimizeEnd;
 end;
 
+// While a --tray launch is still starting up, every top-level window our
+// process shows gets hidden again immediately. Scoped to our process by the
+// hook itself; WebView2 runs in separate processes so its windows never reach
+// here. Torn down as soon as startup finishes.
+procedure TrayShowEventProc(hWinEventHook: THandle; AEvent: DWORD; AWnd: HWND;
+  idObject, idChild: LongInt; idEventThread, dwmsEventTime: DWORD); stdcall;
+begin
+  if not GTrayStartupPending then Exit;
+  if (idObject <> OBJID_WINDOW) or (AWnd = 0) then Exit;
+  if GetParent(AWnd) <> 0 then Exit;          // top-level windows only
+  ShowWindow(AWnd, SW_HIDE);
+end;
+
 procedure TMainForm.TrayHideNow(const ATag: string);
 var
   LHwnd, LAppHwnd: HWND;