feat: add ATL animation timelines and try/raise to the Ren'Py player

Python sandbox
- try/except/else/finally, raise (incl. re-raise), assert, for/while ... else
- Multi-generator and dict comprehensions
- Builtin exception hierarchy; user exceptions subclass it
- Inside try, missing keys/indexes, division by zero, attribute access on None
  and unknown names raise Python exceptions; lookups stay lenient elsewhere
- int()/float() raise ValueError on non-numeric strings

ATL
- converter/atl.py: set/move (linear, ease, easein, easeout), pause, repeat,
  parallel, choice, block, on show/hide and named transforms become a timeline
  shipped as game.json "atl"; Move() becomes a linear slide
- player/atl.ts: timeline runner wired into the renderer; `on hide` plays
  before the picture is removed
- function, time, contains, matrixcolor and expressions still block the import

Tests: exceptions/ATL fixtures and runtime tests, converter ATL tests; README
and ARCHITECTURE updated.

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

frontend/tests/python-classes.test.mjs

@@ -14,7 +14,7 @@ const ir = (name) => JSON.parse(readFileSync(new URL(`./fixtures/${name}.ir.json
 function runtime() {
   const store = Object.create(null);
   const builtins = {
-    any: (xs) => xs.some(Boolean), max: Math.max, int: Number, str: pyStr, list: (xs = []) => [...xs],
+    any: (xs) => xs.some(Boolean), range: (n) => Array.from({ length: n }, (_, i) => i), max: Math.max, int: Number, str: pyStr, list: (xs = []) => [...xs],
   };
   const scope = {
     get: (n) => (n in store ? store[n] : builtins[n]),
@@ -82,3 +82,31 @@ test("unbounded recursion and bad calls fail with explicit errors", () => {
   assert.throws(() => py.eval({ k: "call", f: { k: "name", id: "one" },
     a: [{ k: "const", v: 1 }, { k: "const", v: 2 }], kw: {} }), /слишком много/);
 });
+
+test("try/except/else/finally, raise, loop else, assert and multi-generator comprehensions", () => {
+  const { py, store } = runtime();
+  py.exec(ir("exceptions"));
+  assert.deepEqual(store.log, ["zero", "fin"]);
+  assert.equal(store.result_code, 7);
+  assert.equal(store.result_key, "keyerror"); // dict[...] is strict inside try
+  assert.equal(store.result_index, "indexerror");
+  assert.equal(store.result_value, "valueerror"); // int("abc")
+  assert.equal(store.result_generic, true);
+  assert.equal(store.result_zero, "zerodiv");
+  assert.equal(store.result_retry, 2); // return/continue pass through try
+  assert.equal(store.result_forelse, "none");
+  assert.equal(store.result_whileelse, 30);
+  assert.equal(store.result_reraise, "inner");
+  assert.deepEqual(store.result_pairs, [[1, 3], [1, 4], [2, 3], [2, 4]]);
+  assert.deepEqual([...store.result_dictcomp.map.entries()], [[2, 20]]);
+  assert.equal(store.result_assert, "boom");
+});
+
+test("lookups stay lenient outside try, uncaught exceptions are explicit errors", () => {
+  const { py, store } = runtime();
+  py.exec([{ op: "set", t: { k: "name", id: "d" }, v: { k: "dict", v: [] } }]);
+  assert.equal(py.eval({ k: "sub", o: { k: "name", id: "d" }, i: { k: "const", v: "missing" } }), null);
+  assert.throws(() => py.exec([{ op: "raise", v: { k: "name", id: "ValueError" } }]), /ValueError/);
+  assert.equal(py.strict, 0);
+  void store;
+});