Redesign UI like Driver Navigator + fix CMD window

UI changes:
- Top title bar with logo, app name, and system status LED
- Toolbar with 4 icon tabs: Scan, Drivers, Download, System
- Scan page with computer SVG illustration, stats, and big SCAN NOW button
- Step indicator bar: Scan Devices > Review Drivers > Install Updates
- Driver list with per-row progress bars, Download + Install buttons
- "Update All Drivers" CTA bar at bottom when outdated drivers found
- Windows Update tab with pending/installed sections
- System Info tab with resource bars
- Footer with About/Help buttons

Backend fixes:
- Add cmdutil.HiddenCommand() using CREATE_NO_WINDOW (0x08000000)
- All PowerShell subprocesses now run without visible console window
- Build with -ldflags "-H windowsgui" to hide main CMD window

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/cmdutil/cmdutil.go

@@ -0,0 +1,16 @@
+package cmdutil
+
+import (
+	"os/exec"
+	"syscall"
+)
+
+// HiddenCommand creates an exec.Cmd that runs without showing a console window.
+// This prevents PowerShell/cmd flashing when the app runs as a GUI application.
+func HiddenCommand(name string, args ...string) *exec.Cmd {
+	cmd := exec.Command(name, args...)
+	cmd.SysProcAttr = &syscall.SysProcAttr{
+		CreationFlags: 0x08000000, // CREATE_NO_WINDOW
+	}
+	return cmd
+}