feat: Complete pipeline hot-rebuild implementation with acceptance tests

- Implements pipeline hot-rebuild with state preservation (issue #43)
- Adds auto-injection of MVP stages for missing capabilities
- Adds radial camera mode for polar coordinate scanning
- Adds afterimage and motionblur effects using framebuffer history
- Adds comprehensive acceptance tests for camera modes and pipeline rebuild
- Updates presets.toml with new effect configurations

Related to: #35 (Pipeline Mutation API epic)
Closes: #43, #44, #45

tests/test_display.py

@@ -120,12 +120,16 @@ class TestTerminalDisplay:
 
     def test_get_dimensions_returns_cached_value(self):
         """get_dimensions returns cached dimensions for stability."""
-        display = TerminalDisplay()
-        display.init(80, 24)
+        import os
+        from unittest.mock import patch
 
-        # First call should set cache
-        d1 = display.get_dimensions()
-        assert d1 == (80, 24)
+        # Mock terminal size to ensure deterministic dimensions
+        term_size = os.terminal_size((80, 24))
+        with patch("os.get_terminal_size", return_value=term_size):
+            display = TerminalDisplay()
+            display.init(80, 24)
+            d1 = display.get_dimensions()
+            assert d1 == (80, 24)
 
     def test_show_clears_screen_before_each_frame(self):
         """show clears previous frame to prevent visual wobble.