feat(display): add reuse flag to Display protocol

- Add reuse parameter to Display.init() for all backends
- PygameDisplay: reuse existing SDL window via class-level flag
- TerminalDisplay: skip re-init when reuse=True
- WebSocketDisplay: skip server start when reuse=True
- SixelDisplay, KittyDisplay, NullDisplay: ignore reuse (not applicable)
- MultiDisplay: pass reuse to child displays
- Update benchmark.py to reuse pygame display for effect benchmarks
- Add test_websocket_e2e.py with e2e marker
- Register e2e marker in pyproject.toml

engine/controller.py

@@ -5,8 +5,10 @@ Stream controller - manages input sources and orchestrates the render stream.
 from engine.config import Config, get_config
 from engine.display import (
     DisplayRegistry,
+    KittyDisplay,
     MultiDisplay,
     NullDisplay,
+    PygameDisplay,
     SixelDisplay,
     TerminalDisplay,
     WebSocketDisplay,
@@ -38,6 +40,12 @@ def _get_display(config: Config):
     if display_mode == "sixel":
         displays.append(SixelDisplay())
 
+    if display_mode == "kitty":
+        displays.append(KittyDisplay())
+
+    if display_mode == "pygame":
+        displays.append(PygameDisplay())
+
     if not displays:
         return NullDisplay()