[b-re-w]

Closes #307

• The walker no longer declines a @composable member of a Kotlin object. Its thunk loads Owner.INSTANCE (GETSTATIC) and calls the member with INVOKEVIRTUAL, using the walked MethodNode's own name and descriptor, so there is no name lookup (rule 12.4). Value-returning composables already crossed as OBJECT. No public API change: ThunkSpec.onObjectInstance is internal.
• The compose and notebook-e2e fixtures walk androidx.compose.foundation.shape.
• SPEC B-1 and the notebook-e2e README gap rows are updated.
• Tests:
  • ComposableBindingTest: an object composable binds through an instance thunk, and the thunk is run against an ASM probe.
  • ShapeAndColorsRenderTest: Button and Card with RoundedCornerShape__Dp(20) and red buttonColors/cardColors. The checks are the centre pixel, and the corner of the square control's painted box: red at radius 0, unpainted at 20.
  • ComposableValueClassSlotTest now selects top-level Icon by FQN, because SegmentedButtonDefaults.Icon now binds and has no tint.
• Red check: with the decline put back, the ComposableBindingTest case and both render tests fail.
• Results:
  • Plugin tests: 324/325. The one failure is AcquiredHeaderVersionTest, which depends on build-directory state, is unrelated, and is tracked in Test: AcquiredHeaderVersionTest fails when the 3.15.0 extraction has no ios-arm64 patchlevel #313.
  • Artifact fixture: 44/44. Compose fixture: 125/125.
  • notebook-e2e: compiles, but was not run because no pythonx-compose wheel was given (building one writes into the other repository).