fix(api): list self-aliased providers in canonical models catalog mode (#12381)

GET /v1/models with MODELS_CATALOG_PREFIX_MODE=canonical dropped every chat row of a provider whose registry alias is undefined (antigravity) or equal to its own id (agy, most built-ins). Each emission loop pushes alias/model only when includeAlias, and canonicalProviderId/model only when the ids differ — for a self-aliased provider both are the same string, so neither fired. #11918 fixed the class for custom nodes but not built-ins, and not the static loop. The alias row is now treated as the canonical row whenever the ids coincide, across the static, synced, custom and alias-backed loops; the canonical branch's !== alias guard is untouched, so dual and alias output cannot double up. Docs that described the omission as intended are corrected.

Validated in a combined worktree with all 25 PRs of this batch boarded together: typecheck:core clean, 443/443 node-runner tests plus 14/14 vitest across every test file the batch touches, and check-changelog-integrity, check:cycles (418 files), check:provider-consistency (272 REGISTRY entries, 355 canonical providers), check:docs-counts, check:docs-sync (42 locales) and check-file-size all green.

Thanks @pacocartones.