feat(demo): add HUD effect, resize handling, and tests

- Add HUD effect plugin showing FPS, effect name, intensity bar, pipeline
- Add pygame window resize handling (VIDEORESIZE event)
- Move HUD to end of chain so it renders on top
- Fix monitor stats API (returns dict, not object)
- Add tests/test_hud.py for HUD effect verification

effects_plugins/hud.py

@@ -14,9 +14,11 @@ class HudEffect(EffectPlugin):
         frame_time = 0.0
         if monitor:
             stats = monitor.get_stats()
-            if stats:
-                fps = stats.fps
-                frame_time = stats.avg_frame_time_ms
+            if stats and "pipeline" in stats:
+                frame_time = stats["pipeline"].get("avg_ms", 0.0)
+                frame_count = stats.get("frame_count", 0)
+                if frame_count > 0 and frame_time > 0:
+                    fps = 1000.0 / frame_time
 
         w = ctx.terminal_width
         h = ctx.terminal_height