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

engine/app/main.py

@@ -101,6 +101,8 @@ def run_pipeline_mode_direct():
     border_mode = BorderMode.OFF
     source_items = None
     allow_unsafe = False
+    viewport_width = None
+    viewport_height = None
 
     i = 1
     argv = sys.argv
@@ -115,6 +117,14 @@ def run_pipeline_mode_direct():
         elif arg == "--pipeline-camera" and i + 1 < len(argv):
             camera_type = argv[i + 1]
             i += 2
+        elif arg == "--viewport" and i + 1 < len(argv):
+            vp = argv[i + 1]
+            try:
+                viewport_width, viewport_height = map(int, vp.split("x"))
+            except ValueError:
+                print("Error: Invalid viewport format. Use WxH (e.g., 40x15)")
+                sys.exit(1)
+            i += 2
         elif arg == "--pipeline-display" and i + 1 < len(argv):
             display_name = argv[i + 1]
             i += 2
@@ -221,8 +231,8 @@ def run_pipeline_mode_direct():
 
     # Build pipeline using validated config and params
     params = result.params
-    params.viewport_width = 80
-    params.viewport_height = 24
+    params.viewport_width = viewport_width if viewport_width is not None else 80
+    params.viewport_height = viewport_height if viewport_height is not None else 24
 
     ctx = PipelineContext()
     ctx.params = params
@@ -356,6 +366,12 @@ def run_pipeline_mode_direct():
     current_width = params.viewport_width
     current_height = params.viewport_height
 
+    # Only get dimensions from display if viewport wasn't explicitly set
+    if "--viewport" not in sys.argv and hasattr(display, "get_dimensions"):
+        current_width, current_height = display.get_dimensions()
+        params.viewport_width = current_width
+        params.viewport_height = current_height
+
     print("  \033[38;5;82mStarting pipeline...\033[0m")
     print("  \033[38;5;245mPress Ctrl+C to exit\033[0m\n")