chore(startup): name the WebView2 runtime and mark every milestone

His startup.log stops after 'data dir ok', which rules out the two faults
already covered and leaves the window creation itself — where a missing
WebView2 runtime lands, sometimes as a silent exit rather than an error
anyone can print.

So the runtime's version is read from where it registers itself (both
hives, and the 32-bit view where a per-machine install usually lands) and
written BEFORE the window is attempted: 'WebView2: not found' answers the
whole question in one line. Breadcrumbs now also mark entering wails.Run,
reaching OnStartup, and the window painting — which places any launch
that produces nothing between two known points.

webview2_windows.go

@@ -0,0 +1,49 @@
+//go:build windows
+
+package main
+
+// Is the WebView2 runtime actually installed?
+//
+// It is the one dependency OpsLog cannot ship inside its own executable, and
+// its absence is invisible: the process starts, Wails fails to create the
+// browser environment, and on some machines that failure arrives as a silent
+// exit rather than as an error we can print. So the version is read straight
+// from where the runtime registers itself, and written to the startup log
+// BEFORE the window is attempted — a log that says "WebView2: not found"
+// answers the whole question in one line.
+
+import (
+	"golang.org/x/sys/windows/registry"
+)
+
+// webview2Client is the runtime's own update-client GUID, the key it registers
+// its version under. Documented by Microsoft for exactly this check.
+const webview2Client = `Software\Microsoft\EdgeUpdate\Clients\{F3017226-FE2A-4295-8BDF-00C3A9A7E4C5}`
+
+// webView2Version returns the installed runtime version, or "" if there is none.
+//
+// Both hives: a per-machine install writes to HKLM (and to the WOW6432 view of
+// it on 64-bit Windows, which is where it usually lands), a per-user install to
+// HKCU. Missing all three is the answer that matters.
+func webView2Version() string {
+	type place struct {
+		key    registry.Key
+		access uint32
+	}
+	for _, p := range []place{
+		{registry.CURRENT_USER, registry.QUERY_VALUE},
+		{registry.LOCAL_MACHINE, registry.QUERY_VALUE},
+		{registry.LOCAL_MACHINE, registry.QUERY_VALUE | registry.WOW64_32KEY},
+	} {
+		k, err := registry.OpenKey(p.key, webview2Client, p.access)
+		if err != nil {
+			continue
+		}
+		v, _, err := k.GetStringValue("pv")
+		k.Close()
+		if err == nil && v != "" && v != "0.0.0.0" {
+			return v
+		}
+	}
+	return ""
+}