feat(effects): add plugin architecture for visual effects

- Extract effects as fully decoupled plugins in engine/effects/
- Add EffectConfig, EffectContext dataclasses and EffectPlugin protocol
- Add EffectRegistry for plugin discovery and management
- Add EffectChain for ordered pipeline execution
- Move built-in effects to effects_plugins/ directory
- Add interactive effects config picker during startup
- Add NTFY command handler for /effects commands
- Add tests for effects system (24 new tests)
- Update AGENTS.md with effects plugin documentation
- Add conventional commits section to AGENTS.md

chore: add coverage.xml to .gitignore

engine/app.py

@@ -249,6 +249,110 @@ def pick_font_face():
     print()
 
 
+def pick_effects_config():
+    """Interactive picker for configuring effects pipeline."""
+    import effects_plugins
+    from engine.effects import get_effect_chain, get_registry
+
+    effects_plugins.discover_plugins()
+
+    registry = get_registry()
+    chain = get_effect_chain()
+    chain.set_order(["noise", "fade", "glitch", "firehose"])
+
+    effects = list(registry.list_all().values())
+    if not effects:
+        return
+
+    selected = 0
+    editing_intensity = False
+    intensity_value = 1.0
+
+    def _draw_effects_picker():
+        w = tw()
+        print(CLR, end="")
+        print("\033[1;1H", end="")
+        print("  \033[1;38;5;231mEFFECTS CONFIG\033[0m")
+        print(f"  \033[2;38;5;37m{'─' * (w - 4)}\033[0m")
+        print()
+
+        for i, effect in enumerate(effects):
+            prefix = " > " if i == selected else "   "
+            marker = "[*]" if effect.config.enabled else "[ ]"
+            if editing_intensity and i == selected:
+                print(
+                    f"{prefix}{marker} \033[1;38;5;82m{effect.name}\033[0m: intensity={intensity_value:.2f} (use +/- to adjust, Enter to confirm)"
+                )
+            else:
+                print(
+                    f"{prefix}{marker} {effect.name}: intensity={effect.config.intensity:.2f}"
+                )
+
+        print()
+        print(f"  \033[2;38;5;37m{'─' * (w - 4)}\033[0m")
+        print(
+            "  \033[38;5;245mControls: space=toggle on/off | +/-=adjust intensity | arrows=move | Enter=next effect | q=done\033[0m"
+        )
+
+    def _read_effects_key():
+        ch = sys.stdin.read(1)
+        if ch == "\x03":
+            return "interrupt"
+        if ch in ("\r", "\n"):
+            return "enter"
+        if ch == " ":
+            return "toggle"
+        if ch == "q":
+            return "quit"
+        if ch == "+" or ch == "=":
+            return "up"
+        if ch == "-" or ch == "_":
+            return "down"
+        if ch == "\x1b":
+            c1 = sys.stdin.read(1)
+            if c1 != "[":
+                return None
+            c2 = sys.stdin.read(1)
+            if c2 == "A":
+                return "up"
+            if c2 == "B":
+                return "down"
+            return None
+        return None
+
+    if not sys.stdin.isatty():
+        return
+
+    fd = sys.stdin.fileno()
+    old_settings = termios.tcgetattr(fd)
+    try:
+        tty.setcbreak(fd)
+        while True:
+            _draw_effects_picker()
+            key = _read_effects_key()
+
+            if key == "quit" or key == "enter":
+                break
+            elif key == "up" and editing_intensity:
+                intensity_value = min(1.0, intensity_value + 0.1)
+                effects[selected].config.intensity = intensity_value
+            elif key == "down" and editing_intensity:
+                intensity_value = max(0.0, intensity_value - 0.1)
+                effects[selected].config.intensity = intensity_value
+            elif key == "up":
+                selected = max(0, selected - 1)
+                intensity_value = effects[selected].config.intensity
+            elif key == "down":
+                selected = min(len(effects) - 1, selected + 1)
+                intensity_value = effects[selected].config.intensity
+            elif key == "toggle":
+                effects[selected].config.enabled = not effects[selected].config.enabled
+            elif key == "interrupt":
+                raise KeyboardInterrupt
+    finally:
+        termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
+
+
 def main():
     atexit.register(lambda: print(CURSOR_ON, end="", flush=True))
 
@@ -263,6 +367,7 @@ def main():
     print(CLR, end="")
     print(CURSOR_OFF, end="")
     pick_font_face()
+    pick_effects_config()
     w = tw()
     print()
     time.sleep(0.4)