feat(repl): Add REPL effect with HUD-style interactive interface

Implement a Read-Eval-Print Loop (REPL) effect that provides a
HUD-style overlay for interactive pipeline control.

## New Files

- engine/effects/plugins/repl.py - REPL effect plugin with command processor
- engine/display/backends/terminal.py - Added raw mode and input handling
- examples/repl_simple.py - Simple demonstration script
- tests/test_repl_effect.py - 18 comprehensive tests

## Features

### REPL Interface
- HUD-style overlay showing FPS, command history, output buffer size
- Command history navigation (Up/Down arrows)
- Command execution (Enter)
- Character input and backspace support
- Output buffer with scrolling

### Commands
- help - Show available commands
- status - Show pipeline status and metrics
- effects - List all effects in pipeline
- effect <name> <on|off> - Toggle effect
- param <effect> <param> <value> - Set parameter
- pipeline - Show current pipeline order
- clear - Clear output buffer
- quit - Show exit message

### Terminal Input Support
- Added set_raw_mode() to TerminalDisplay for capturing keystrokes
- Added get_input_keys() to read keyboard input
- Proper terminal state restoration on cleanup

## Usage

Add 'repl' to effects in your configuration:

## Testing

All 18 REPL tests pass, covering:
- Effect registration
- Command processing
- Navigation (history, editing)
- Configuration
- Rendering

## Integration

The REPL effect integrates with the existing pipeline system:
- Uses EffectPlugin interface
- Supports partial updates
- Reads metrics from EffectContext
- Can be controlled via keyboard when terminal display is in raw mode

Next steps:
- Integrate REPL input handling into pipeline_runner.py
- Add keyboard event processing loop
- Create full demo with interactive features

engine/pipeline/hybrid_config.py

@@ -124,22 +124,44 @@ class PipelineConfig:
 
         # Add effect nodes
         for effect in self.effects:
-            graph.node(
-                effect.name,
-                NodeType.EFFECT,
-                effect=effect.name,
-                intensity=effect.intensity,
-                enabled=effect.enabled,
-                **effect.params,
-            )
+            # Handle both EffectConfig objects and dictionaries
+            if isinstance(effect, dict):
+                name = effect.get("name", "")
+                intensity = effect.get("intensity", 1.0)
+                enabled = effect.get("enabled", True)
+                params = effect.get("params", {})
+            else:
+                name = effect.name
+                intensity = effect.intensity
+                enabled = effect.enabled
+                params = effect.params
+
+            if name:
+                graph.node(
+                    name,
+                    NodeType.EFFECT,
+                    effect=name,
+                    intensity=intensity,
+                    enabled=enabled,
+                    **params,
+                )
 
         # Add display node
-        display_config = self.display or DisplayConfig()
+        if isinstance(self.display, dict):
+            display_backend = self.display.get("backend", "terminal")
+            display_positioning = self.display.get("positioning", "mixed")
+        elif self.display:
+            display_backend = self.display.backend
+            display_positioning = self.display.positioning
+        else:
+            display_backend = "terminal"
+            display_positioning = "mixed"
+
         graph.node(
             "display",
             NodeType.DISPLAY,
-            backend=display_config.backend,
-            positioning=display_config.positioning,
+            backend=display_backend,
+            positioning=display_positioning,
         )
 
         # Create linear connections
@@ -151,7 +173,9 @@ class PipelineConfig:
 
         # Add all effects in order
         for effect in self.effects:
-            chain.append(effect.name)
+            name = effect.get("name", "") if isinstance(effect, dict) else effect.name
+            if name:
+                chain.append(name)
 
         chain.append("display")