feat: ATL pictures/contains/function/time, colour matrices and more Python for Ren'Py

ATL
- Image blocks become timelines: picture steps with dissolve, parallel, contains,
  finite repeat, time, function f(trans, st, at), calls of other transforms with
  arguments, on hover/idle events for buttons. Animations stop when their element
  leaves the page
- Pictures defined by an expression (get_face_path("base")) are drawn at show time
- Purely graphical hints (shader, mesh, gl_*, u_*) are accepted and dropped

Colour
- matrixcolor and im.matrix.* as 5x5 matrices combined with `*`, applied through SVG
  filters; im.MatrixColor/Scale/Crop/Blur/Composite and Text/Image as values

Python
- match statement, re/copy/time/datetime/defaultdict/functools.partial, more
  str/dict methods, Character(...) created by code
- narrator("..."), Character calls, renpy.say and renpy.show/hide with expressions in
  Python blocks become script nodes
- Audit follows reachability: functions and classes nothing refers to (custom
  statement lexers, unused tools) no longer block an import

Docs: README and ARCHITECTURE now describe a multi-engine library (GameMaker and
QSP planned). Tests for the new runtime pieces.

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

backend/app/converter/pipeline.py

@@ -344,6 +344,8 @@ def _resolve_image(img: dict[str, Any], aliases: dict[str, str], missing: set[st
     if "frames" in img:
         img["frames"] = [{**f, "img": _resolve_image(f["img"], aliases, missing)}
                          for f in img["frames"]]
+    if "timeline" in img:
+        img["timeline"] = _resolve_timeline(img["timeline"], aliases, missing)
     if "layered" in img:
         layers = []
         for layer in img["layered"]:
@@ -359,6 +361,23 @@ def _resolve_image(img: dict[str, Any], aliases: dict[str, str], missing: set[st
     return img
 
 
+def _resolve_timeline(block: dict[str, Any], aliases: dict[str, str], missing: set[str]) -> dict[str, Any]:
+    """Resolve the pictures an ATL timeline shows."""
+    def step(s: dict[str, Any]) -> dict[str, Any]:
+        s = dict(s)
+        if s["op"] in ("image", "contains"):
+            s["img"] = _resolve_image(s["img"], aliases, missing)
+        elif s["op"] == "parallel":
+            s["blocks"] = [_resolve_timeline(b, aliases, missing) for b in s["blocks"]]
+        elif s["op"] == "choice":
+            s["blocks"] = [{**b, "block": _resolve_timeline(b["block"], aliases, missing)} for b in s["blocks"]]
+        elif s["op"] in ("block", "on"):
+            s["block"] = _resolve_timeline(s["block"], aliases, missing)
+        return s
+
+    return {**block, "steps": [step(s) for s in block["steps"]]}
+
+
 def anchors(labels: list[dict[str, Any]]) -> dict[str, dict[str, Any]]:
     """Positions of `label` markers (nested labels, named menus) inside label bodies."""
     found: dict[str, dict[str, Any]] = {}