[ADC-680] Prove external AOT from the installed wheel

[wolf75222]

Scope

Closes the remaining ADC-680 installed-wheel acceptance gap on top of #634.

The ordinary final gate pins POPS_INCLUDE to the checkout. That is correct for source conformance, but it meant the external AOT package test could pass after wheel installation while still compiling against source-tree headers. This stack adds one exact isolated lane that:

• clears POPS_INCLUDE instead of pointing it at the checkout;
• imports the retained installed wheel with an empty PYTHONPATH;
• requires pops_include() to resolve exactly to Path(pops.__file__).parent / "include";
• refuses a stub/mock route by requiring the installed extension file, Kokkos native capability, and native-loader schema;
• compiles, installs, loads, and invokes the exact external numerical-flux component node;
• retains a one-test JUnit report and rejects skip, xfail, duplicate node execution, source-header override, command drift, and digest drift during release preflight.

History

Five thematic commits are preserved: gate implementation, evidence-audit extraction, tests, documentation, and a Path-to-POSIX fix exposed by the new preflight test. No squash, rebase, amend, or force-push was used.

Source-only validation

• 44 passed: final release gate, release contract, codesign scripts, release matrix preflight
• 7 passed: strict source/fixed component package contracts
• Ruff: passed on all changed Python files
• compileall: passed
• release and component generators: clean
• docs checker: passed (one pre-existing freshness warning)
• git diff --check: passed

Deliberate non-claim

No shared native build or release wheel was produced locally. The exact installed-wheel AOT execution is now a fail-closed release-gate requirement and remains to be executed by the real macOS arm64/cp312 release lane after #634 and this stack are integrated.