feat(positioning): Add configurable PositionStage for positioning modes

- Added PositioningMode enum (ABSOLUTE, RELATIVE, MIXED)
- Created PositionStage class with configurable positioning modes
- Updated terminal display to support positioning parameter
- Updated PipelineParams to include positioning field
- Updated DisplayStage to pass positioning to terminal display
- Added documentation in docs/positioning-analysis.md

Positioning modes:
- ABSOLUTE: Each line has cursor positioning codes (\033[row;1H)
- RELATIVE: Lines use newlines (no cursor codes, better for scrolling)
- MIXED: Base content uses newlines, effects use absolute positioning (default)

Usage:
  # In pipeline or preset:
  positioning = "absolute"  # or "relative" or "mixed"

  # Via command line (future):
  --positioning absolute

engine/pipeline/adapters/display.py

@@ -8,7 +8,7 @@ from engine.pipeline.core import PipelineContext, Stage
 class DisplayStage(Stage):
     """Adapter wrapping Display as a Stage."""
 
-    def __init__(self, display, name: str = "terminal"):
+    def __init__(self, display, name: str = "terminal", positioning: str = "mixed"):
         self._display = display
         self.name = name
         self.category = "display"
@@ -16,6 +16,7 @@ class DisplayStage(Stage):
         self._initialized = False
         self._init_width = 80
         self._init_height = 24
+        self._positioning = positioning
 
     def save_state(self) -> dict[str, Any]:
         """Save display state for restoration after pipeline rebuild.
@@ -87,7 +88,20 @@ class DisplayStage(Stage):
     def process(self, data: Any, ctx: PipelineContext) -> Any:
         """Output data to display."""
         if data is not None:
-            self._display.show(data)
+            # Check if positioning mode is specified in context params
+            positioning = self._positioning
+            if ctx and ctx.params and hasattr(ctx.params, "positioning"):
+                positioning = ctx.params.positioning
+
+            # Pass positioning to display if supported
+            if (
+                hasattr(self._display, "show")
+                and "positioning" in self._display.show.__code__.co_varnames
+            ):
+                self._display.show(data, positioning=positioning)
+            else:
+                # Fallback for displays that don't support positioning parameter
+                self._display.show(data)
         return data
 
     def cleanup(self) -> None: