fix(startup): report a window that never opens

The data folder is created and stays empty, the process keeps running,
and no window appears. Nothing returns, so nothing is logged: WebView2
never hands control back, and a hang has no error to report.

So the ABSENCE of progress is reported. If OnStartup has not been reached
twelve seconds after wails.Run, that is written to the startup log and
shown in a message box naming the two causes — a missing WebView2 runtime
and an antivirus blocking msedgewebview2.exe — because 'OpsLog is not
responding' otherwise sends people to reinstall OpsLog, which is the one
thing that cannot help: the part that has not started is not ours.

app.go

@@ -997,6 +997,7 @@ func (a *App) startup(ctx context.Context) {
 	// One line in the startup log too, not only in OpsLog's own: the two
 	// together say whether a launch that produced no window got as far as our
 	// code at all, which is the fork every "it does not start" report turns on.
+	startupReached.Store(true)
 	bootLog("OnStartup reached")
 
 	dataDir, err := userDataDir()

bootlog.go

@@ -19,6 +19,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"sync/atomic"
 	"time"
 )
 
@@ -93,3 +94,18 @@ func checkDataDirWritable() error {
 	bootLog("data dir ok: %s", dir)
 	return nil
 }
+
+// startupReached flips as soon as OnStartup runs — the first moment OpsLog's
+// own code is executing inside the window's lifecycle.
+var startupReached atomic.Bool
+
+// startupStuckMessage is what an operator sees when the window never starts.
+//
+// It names the two causes and what to do about each, because "OpsLog is not
+// responding" sends people to reinstall OpsLog, which is the one thing that
+// cannot help: the part that has not started is not ours.
+const startupStuckMessage = "OpsLog started but its window never opened.\n\n" +
+	"This is the WebView2 runtime failing to start, and it is almost always one of two things:\n\n" +
+	"• The Microsoft Edge WebView2 Runtime is missing — install it from Microsoft, then start OpsLog again.\n" +
+	"• An antivirus is blocking msedgewebview2.exe — add OpsLog's folder to its exceptions.\n\n" +
+	"The details are in the OpsLog folder under LOCALAPPDATA (startup.log)."

main.go

@@ -145,6 +145,23 @@ func main() {
 	}
 
 	// Create application with options
+	// A HANG has no error to report, and that is the shape being chased here:
+	// the process stays up, the data folder is created and stays empty, and no
+	// window appears — WebView2 never finishes creating its environment, and
+	// nothing returns to be logged.
+	//
+	// So the absence of progress is what gets reported. If OnStartup has not
+	// been reached a few seconds in, this says so and names the two things that
+	// cause it, rather than leaving an operator watching a process that is doing
+	// nothing at all.
+	go func() {
+		time.Sleep(12 * time.Second)
+		if startupReached.Load() {
+			return
+		}
+		bootLog("STUCK: 12 s after wails.Run and the window has not started — WebView2 never handed control back")
+		fatalBox("OpsLog", startupStuckMessage)
+	}()
 	bootLog("entering wails.Run (window %dx%d, state %v)", width, height, startState)
 	err := wails.Run(&options.App{
 		Title:            "OpsLog",