feat: Ren'Py screens (screen/call screen/show screen) with actions and styles

Converter
- screens.py parses the screen language: containers (fixed, frame, vbox, hbox,
  grid, vpgrid, viewport, button, has), widgets (text, textbutton, imagebutton,
  add, bar ...), if/for/use/transclude, default, python, key, timer, on, inline ATL,
  conditional properties, and decompiled forms (unparenthesised operators,
  glued property values, comma separated actions)
- style statements, call/show/hide screen operators and Python-level
  renpy.show_screen are translated; only screens the game shows are audited,
  unused stock screens no longer block an import; undefined screens do
- ATL values may be computed at run time and transforms take parameters
  (at blink(0.2, 0.3)); blur property

Player
- screens.ts builds the DOM from the IR and rebuilds it on state changes;
  buttons with idle/hover/selected/insensitive states, tooltips, sounds, modal
  screens, timers and keys that survive re-rendering, saved with the save file
- Actions: Jump, Call, Return, SetVariable, Toggle*, SetScreenVariable, Show, Hide,
  ToggleScreen, Function, Play, Notify, If, Language, ShowMenu, OpenURL ...
- Crop/LiveCrop/Solid/Frame/Transform/DynamicDisplayable values, crop property,
  globals(), renpy.variant/change_language/seen_image, transition stubs

Tests: screen parser and runtime (linkedom DOM), screens fixture compiled from
tests/fixtures/screens.rpy. Docs: docs/SCREENS.md.

Twisted-Thoughts now passes the strict compatibility check.

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

backend/tests/make_screens.py

@@ -0,0 +1,23 @@
+"""Compile the screens/styles of a .rpy file to JSON: python -m tests.make_screens SOURCE.rpy OUT.json"""
+import json
+import sys
+from pathlib import Path
+
+from app.converter.compatibility import audit_ir, require_supported_scripts
+from app.converter.pipeline import _used_screens
+from app.converter.rpy_parser import RpyParser, ScriptData
+
+
+def main(source: Path, out: Path) -> None:
+    data = ScriptData()
+    RpyParser(data, source.name).parse(source.read_text(encoding="utf-8"))
+    audit_ir(data)
+    require_supported_scripts(data)
+    shipped = {name: data.screens[name] for name in sorted(_used_screens(data))}
+    out.write_text(json.dumps({"screens": shipped, "styles": data.styles, "atl": data.atl,
+                               "transforms": data.transforms}, ensure_ascii=False, separators=(",", ":")),
+                   encoding="utf-8")
+
+
+if __name__ == "__main__":
+    main(Path(sys.argv[1]), Path(sys.argv[2]))