fix: resolve terminal display wobble and effect dimension stability

- Fix TerminalDisplay: add screen clear each frame (cursor home + erase down)
- Fix CameraStage: use set_canvas_size instead of read-only viewport properties
- Fix Glitch effect: preserve visible line lengths, remove cursor positioning
- Fix Fade effect: return original line when fade=0 instead of empty string
- Fix Noise effect: use input line length instead of terminal_width
- Remove HUD effect from all presets (redundant with border FPS display)
- Add regression tests for effect dimension stability
- Add docs/ARCHITECTURE.md with Mermaid diagrams
- Add mise tasks: diagram-ascii, diagram-validate, diagram-check
- Move markdown docs to docs/ (ARCHITECTURE, Refactor, hardware specs)
- Remove redundant requirements files (use pyproject.toml)
- Add *.dot and *.png to .gitignore

Closes #25

engine/pipeline/adapters.py

@@ -347,9 +347,12 @@ class CameraStage(Stage):
             )
 
             # Update camera's viewport dimensions so it knows its actual bounds
-            if hasattr(self._camera, "viewport_width"):
-                self._camera.viewport_width = viewport_width
-                self._camera.viewport_height = viewport_height
+            # Set canvas size to achieve desired viewport (viewport = canvas / zoom)
+            if hasattr(self._camera, "set_canvas_size"):
+                self._camera.set_canvas_size(
+                    width=int(viewport_width * self._camera.zoom),
+                    height=int(viewport_height * self._camera.zoom),
+                )
 
             # Set canvas to full layout height so camera can scroll through all content
             self._camera.set_canvas_size(width=canvas_width, height=total_layout_height)