fix(resolve): refuse unstable Python captured receivers - #403

A Python closure can read a different receiver value when invoked than the value present at its definition. After store = A(), defining a closure that calls store.get(), then assigning store = B(), the graph previously linked the closure to A.get.

The resolver now leaves captured calls and method values unlinked when a later indexed replacement makes the invocation-time receiver uncertain. It preserves direct local reassignment, a single future initialization, bare annotations, and imports that add another submodule to the same package. This conservative rule can omit valid calls made before a later replacement. It does not track arbitrary writes through other closures or dynamic mutation.

This follows the lexical receiver work in #395. The README's About this fork Python receiver bullet and the languages reference describe the new boundary; the language inventory, upstream merge point and measured-result rows are unchanged.

Validation on Node 24:

• Eight original mutation regressions fail with the baseline kernel. Five additional review regressions fail with the previous guard. The candidate passes all 118 focused tests, including stable self/cls, lambda defaults, generator iterable evaluation and captured method values.
• Native release build, Clippy and application build pass.
• All 13 golden/README checks pass; regeneration changes no dumps.
• Flask, Vite and Gin precision controls pass. Complete call/reference comparisons find no lost or gained edges in any corpus.
• Full suite passes: 606 files, 7,790 tests, 39 existing skips. Test-floor and whitespace checks pass.

Collapsed receiver names and deferred lambda/generator scopes were fixed after the initial review. Focused regressions and the required checks verify those fixes; no further review round ran.