Working prototype with dev dashboard

- Created core Engine that coordinates all subsystems
- Extended API with comprehensive endpoints for dev dashboard
- Implemented pure Go vision processing (no GoCV dependency)
- Built full-featured dev dashboard with live capture viewer, region overlays, pixel inspector
- Added D2R detector with actual health/mana reading from orb regions
- Fixed resolution profile registration and region validation
- Generated synthetic test data for development
- Added dev mode support with file backend for testing
- Fixed build tag issues for cross-platform compilation

Prototype features:
✅ Live capture viewer with region overlays
✅ Real-time state detection (game state, health %, mana %)
✅ Pixel inspector (hover for RGB/HSV values)
✅ Capture stats monitoring (FPS, frame count)
✅ Region management with toggle visibility
✅ File upload for testing screenshots
✅ Dark theme dev-focused UI
✅ CORS enabled for dev convenience

Ready for: go run ./cmd/iso-bot --dev --api :8080

pkg/engine/capture/backends/stubs.go

@@ -0,0 +1,15 @@
+// Helper functions for backends
+package backends
+
+import "runtime"
+
+// MonitorSourceAvailable returns true if monitor capture is available on this platform.
+func MonitorSourceAvailable() bool {
+	// Monitor capture should work on most platforms, but let's be conservative
+	switch runtime.GOOS {
+	case "windows", "linux", "darwin":
+		return true
+	default:
+		return false
+	}
+}