feat: Implement Sideline plugin system with consistent terminology

This commit implements the Sideline/Mainline split with a clean plugin architecture:

## Core Changes

### Sideline Framework (New Directory)
- Created  directory containing the reusable pipeline framework
- Moved pipeline core, controllers, adapters, and registry to
- Moved display system to
- Moved effects system to
- Created plugin system with security and compatibility management in
- Created preset pack system with ASCII art encoding in
- Added default font (Corptic) to
- Added terminal ANSI constants to

### Mainline Application (Updated)
- Created  for Mainline stage component registration
- Updated  to register Mainline stages at startup
- Updated  as a compatibility shim re-exporting from sideline

### Terminology Consistency
- : Base class for all pipeline components (sources, effects, displays, cameras)
- : Base class for distributable plugin packages (was )
- : Base class for visual effects (was )
- Backward compatibility aliases maintained for existing code

## Key Features
- Plugin discovery via entry points and explicit registration
- Security permissions system for plugins
- Compatibility management with semantic version constraints
- Preset pack system for distributable configurations
- Default font bundled with Sideline (Corptic.otf)

## Testing
- Updated tests to register Mainline stages before discovery
- All StageRegistry tests passing

Note: This is a major refactoring that separates the framework (Sideline) from the application (Mainline), enabling Sideline to be used by other applications.

sideline/effects/__init__.py

@@ -0,0 +1,27 @@
+from sideline.effects.chain import EffectChain
+from sideline.effects.performance import PerformanceMonitor, get_monitor, set_monitor
+from sideline.effects.registry import EffectRegistry, get_registry, set_registry
+from sideline.effects.types import (
+    EffectConfig,
+    EffectContext,
+    Effect,
+    EffectPlugin,  # Backward compatibility alias
+    create_effect_context,
+)
+
+# Note: Legacy effects and controller are Mainline-specific and moved to engine/effects/
+
+__all__ = [
+    "EffectChain",
+    "EffectRegistry",
+    "EffectConfig",
+    "EffectContext",
+    "Effect",  # Primary class name
+    "EffectPlugin",  # Backward compatibility alias
+    "create_effect_context",
+    "get_registry",
+    "set_registry",
+    "get_monitor",
+    "set_monitor",
+    "PerformanceMonitor",
+]