ADC-681: resolve Reflux through the public AMR provider protocol

[wolf75222]

Stack

This draft is stacked on #638, which is itself stacked on #617. All existing code, test, documentation, and merge commits are preserved; this branch adds exactly three thematic commits.

Strict audit result

Current master does not contain the #617/#638 commits. Across master + #617 + #638, the generated Reflux ABI, prepared adapter, local execution, PoPS-owned collective publication, and internal pybind installation seam exist. The first confirmed remaining source gap was the explicit one documented by #638: Reflux was not part of normalized public AMR provider resolution, so only clustering and tagger crossed resolve/compile/bind.

What changed

• add public RefluxProvider(component=...) authoring and builtin FluxRegisterReflux;
• add AMR(..., reflux=...) with the builtin as its explicit default authority;
• authenticate layout and Program-clock identity through the Reflux-native interface protocol;
• carry the role in canonical order through resolution, plan validation, compiled provenance, runtime reports, and the existing transactional installer from [ADC-681] Execute prepared Reflux components in AMR transitions #638;
• keep central runtime installation generic: it reads component_installer from the native-interface protocol rather than branching on a concrete provider class;
• reject absent external Reflux component authorities before any installer runs.

Validation

• 50/50 targeted external-provider, public-resolution, and Reflux architecture tests passed;
• 20/20 affected layout-plan and descriptor tests passed;
• Ruff checks passed;
• Python compileall passed;
• generated component catalog drift check passed;
• docs check passed with one pre-existing stale-dependency warning;
• git diff --check passed.

The native introspection test was intentionally not run: this isolated worktree has no locally built _pops extension and the root native build was left untouched.

Deliberate non-claims / remaining ADC-681 work

• no native rebuild or installed-package proof in this slice;
• no real external Reflux execution under multi-rank MPI;
• no numerical conservation/regrid/rank-count qualification for the external component route;
• no GPU execution; the prepared Reflux v1 adapter remains explicitly fail-closed outside 2D float64 host storage;
• ADC-681 therefore remains In Progress.