test(stage2): register ownership schema suite + add round-trip fixture

The previous session wrote the ownership schema tests (find_ownership_section,
parse_ownership_section, test_ownership_*) but did not register them in the
test suite list and did not include the required fixture file.

This commit wires the three loose ends:
- `test/e2e/fixtures/ownership_codegen.affine` — four functions covering all
  four ownership kinds: own/ref/mut/plain
- `test/test_e2e.ml` — adds `("E2E Ownership Schema", ownership_schema_tests)`
  to the test registry

All 78 tests pass (3 new ownership schema round-trip tests included).

Stage 2 is now fully closed:
  ✓ 2a: TOwn/TRef/TMut → typed-wasm kind mapping designed
  ✓ 2b: [affinescript.ownership] custom section emitted in codegen
  ✓ 2c: schema reader (parse_ownership_section in test_e2e.ml)
  ✓ 2d: round-trip integration test: compile → emit → parse → verify kinds

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: hyperpolymath

test/e2e/fixtures/ownership_codegen.affine

@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: PMPL-1.0-or-later
+// Stage 2 round-trip test fixture.
+// Ownership annotations must survive from AffineScript source to the Wasm custom section.
+// Bodies return literals to avoid type unification between own/ref/mut and the plain return type.
+
+fn consume_owned(x: own Int) -> Int {
+  0
+}
+
+fn borrow_ref(y: ref Int) -> Int {
+  0
+}
+
+fn borrow_mut(z: mut Int) -> Int {
+  0
+}
+
+fn plain(n: Int) -> Int {
+  0
+}

test/test_e2e.ml

@@ -1149,6 +1149,7 @@ let tests =
     ("E2E Quantity", quantity_tests);
     ("E2E Linear Arrows", linear_arrow_tests);
     ("E2E WASM", wasm_tests);
+    ("E2E Ownership Schema", ownership_schema_tests);
     ("E2E Julia", julia_tests);
     ("E2E Interp", interp_tests);
     ("E2E Optimizer", optimizer_tests);