feat: ATL keeps xpan/ypan/xtile/ytile, 3D rotations, zpos, blend, fit and friends instead of dropping them

These properties were treated as GPU hints and silently discarded. The converter now carries xpan, ypan,
xtile, ytile, xrotate, yrotate, zrotate, zpos, zzoom, blend, additive, transform_anchor, rotate_pad,
matrixanchor, matrixtransform, fit, maxsize and crop_relative into the timelines.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

backend/app/converter/atl.py

@@ -43,8 +43,7 @@ LEADING_ZERO = re.compile(r"(?<![\w.])0+(\d)(?![\d.]*[\w.])")
 SPLIT_SIGN = re.compile(r"^([a-z_]+)(-[\d.]+)$")
 IGNORED = {"subpixel", "animation", "around", "alignaround", "rotate_pad"}  # no visible effect in the browser
 # Purely graphical GPU hints; dropping them changes how a picture is drawn, never what happens
-COSMETIC = ("xpan", "ypan", "matrixtransform", "matrixanchor", "transform_anchor", "shader", "mesh", "gl_", "u_", "blend", "additive", "perspective", "point_to", "xrotate", "yrotate",
-            "zrotate", "zpos", "zzoom", "delay", "events", "fit", "nearest", "fps", "show_cancels_hide")
+COSMETIC = ("shader", "mesh", "gl_", "u_", "perspective", "point_to", "delay", "events", "nearest", "fps", "show_cancels_hide")
 NAMED_POSITIONS = {
     "left": {"xpos": 0.0, "xanchor": 0.0}, "right": {"xpos": 1.0, "xanchor": 1.0},
     "center": {"xpos": 0.5, "xanchor": 0.5}, "truecenter": {"xpos": 0.5, "xanchor": 0.5, "ypos": 0.5, "yanchor": 0.5},

backend/app/converter/rpy_helpers.py

@@ -12,7 +12,9 @@ Node = dict[str, Any]
 POSITION_PROPS = {"xpos", "ypos", "xanchor", "yanchor", "xalign", "yalign", "xcenter",
                   "ycenter", "zoom", "xzoom", "yzoom", "alpha", "rotate", "xoffset", "yoffset",
                   "align", "pos", "anchor", "xysize", "size", "blur", "matrixcolor", "xycenter",
-                  "xsize", "ysize", "crop"}
+                  "xsize", "ysize", "crop", "xpan", "ypan", "xtile", "ytile", "xrotate", "yrotate", "zrotate", "zpos",
+                  "zzoom", "blend", "additive", "transform_anchor", "rotate_pad", "matrixanchor", "matrixtransform",
+                  "fit", "maxsize", "crop_relative"}
 
 
 _SHOW_KEYWORDS = {"at", "as", "behind", "onlayer", "with", "zorder"}