Calculation fixes based on user feedback.

- Overlay lines at every aspect ratio: lines are now drawn with Blender's polyline shader. Vertical and horizontal lines no longer disappear (Blender 5.x, lens shift), and Line Width now works on every GPU backend.
- Golden Spiral: rebuilt in the frame's real proportions. Squares stay square and arcs stay circular at 16:9, 2.39:1, 9:16 and with non-square pixels. Portrait frames get a portrait spiral, and the arcs now connect into one continuous curve. Spiral Rotation picks the corner the spiral curls into.
- Aspect presets with pixel aspect: the render resolution sync now targets the displayed ratio, so gates stay correct with anamorphic pixel aspect.
- Letterbox: filled with triangles instead of the deprecated triangle fan.
- Smart Frame: shot size distance now uses the true vertical frame size (sensor fit, render aspect, pixel aspect). It previously always used the sensor height, so shots came out too wide or too tight at most aspect ratios.
- Thirds placement respects lens shift and the render aspect, and no longer uses the camera rotation from the previous shot.
- Headroom now moves the subject down (it moved it up before) and scales with the real camera distance.