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/terminal.py

@@ -0,0 +1,108 @@
+"""
+ANSI escape codes and terminal control constants.
+
+Provides standard ANSI escape sequences for terminal manipulation.
+This module belongs in Sideline as it's a framework-level concern.
+"""
+
+# ─── ANSI RESET ──────────────────────────────────────────
+RST = "\033[0m"
+
+# ─── TEXT STYLES ─────────────────────────────────────────
+BOLD = "\033[1m"
+DIM = "\033[2m"
+UNDERLINE = "\033[4m"
+REVERSE = "\033[7m"
+
+# ─── MATRIX GREENS (Sideline default theme) ─────────────
+G_HI = "\033[38;5;46m"  # Bright green
+G_MID = "\033[38;5;34m"  # Medium green
+G_LO = "\033[38;5;22m"  # Dark green
+G_DIM = "\033[2;38;5;34m"  # Dim green
+
+# ─── COOL TONES ──────────────────────────────────────────
+W_COOL = "\033[38;5;250m"  # Cool white
+W_DIM = "\033[2;38;5;245m"  # Dim white
+W_GHOST = "\033[2;38;5;238m"  # Ghost white
+C_DIM = "\033[2;38;5;37m"  # Dim cyan
+
+# ─── TERMINAL CONTROL ────────────────────────────────────
+CLR = "\033[2J\033[H"  # Clear screen and home cursor
+CURSOR_OFF = "\033[?25l"  # Hide cursor
+CURSOR_ON = "\033[?25h"  # Show cursor
+
+
+# ─── CURSOR POSITIONING ──────────────────────────────────
+def cursor_pos(row: int, col: int) -> str:
+    """Move cursor to position (row, col)."""
+    return f"\033[{row};{col}H"
+
+
+# ─── COLOR UTILITIES ─────────────────────────────────────
+def fg_color(code: int) -> str:
+    """Set foreground color (0-255)."""
+    return f"\033[38;5;{code}m"
+
+
+def bg_color(code: int) -> str:
+    """Set background color (0-255)."""
+    return f"\033[48;5;{code}m"
+
+
+# ─── COMMON COLORS ───────────────────────────────────────
+BLACK = "\033[30m"
+RED = "\033[31m"
+GREEN = "\033[32m"
+YELLOW = "\033[33m"
+BLUE = "\033[34m"
+MAGENTA = "\033[35m"
+CYAN = "\033[36m"
+WHITE = "\033[37m"
+
+# ─── BRIGHT COLORS ───────────────────────────────────────
+BRIGHT_BLACK = "\033[90m"
+BRIGHT_RED = "\033[91m"
+BRIGHT_GREEN = "\033[92m"
+BRIGHT_YELLOW = "\033[93m"
+BRIGHT_BLUE = "\033[94m"
+BRIGHT_MAGENTA = "\033[95m"
+BRIGHT_CYAN = "\033[96m"
+BRIGHT_WHITE = "\033[97m"
+
+__all__ = [
+    "RST",
+    "BOLD",
+    "DIM",
+    "UNDERLINE",
+    "REVERSE",
+    "G_HI",
+    "G_MID",
+    "G_LO",
+    "G_DIM",
+    "W_COOL",
+    "W_DIM",
+    "W_GHOST",
+    "C_DIM",
+    "CLR",
+    "CURSOR_OFF",
+    "CURSOR_ON",
+    "cursor_pos",
+    "fg_color",
+    "bg_color",
+    "BLACK",
+    "RED",
+    "GREEN",
+    "YELLOW",
+    "BLUE",
+    "MAGENTA",
+    "CYAN",
+    "WHITE",
+    "BRIGHT_BLACK",
+    "BRIGHT_RED",
+    "BRIGHT_GREEN",
+    "BRIGHT_YELLOW",
+    "BRIGHT_BLUE",
+    "BRIGHT_MAGENTA",
+    "BRIGHT_CYAN",
+    "BRIGHT_WHITE",
+]