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

[pacocartones]

Summary

• GET /v1/models with MODELS_CATALOG_PREFIX_MODE=canonical (or ?prefix=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. fix(models): expose custom node models in canonical prefix mode (#11832) #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 (selfAliased), in the static, synced, custom and alias-backed loops; the canonical branch's !== alias guard is untouched, so dual and alias output are unchanged and cannot double up. Docs that described the omission as intended are updated.

Related Issues

• Closes fix(api): Antigravity models not listed when MODELS_CATALOG_PREFIX_MODE=Canonical #12058
• Related to fix(api): custom-prefixed node models omitted from /v1/models under canonical prefix mode #11832, fix(models): expose custom node models in canonical prefix mode (#11832) #11918

Validation

• Change type: provider / routing
• Focused tests and category gates from the golden path: tests/unit/12058-models-catalog-canonical-self-aliased.test.ts RED 3/4 on the base, GREEN 4/4 with the fix; per-site mutation check (4 sites killed, overshoot mutant killed); the 68 catalog-importing unit files 417/418 (the one failure, 9147-catalog-eventloop-yield, fails identically on the unmodified base: environment timing); npm run typecheck:core 0; check:changelog-integrity OK; check:env-doc-sync OK; check:docs-sync OK
• npm run lint — repository-wide eslint exit 0 (run with --pass-on-unpruned-suppressions; the literal command reports only pre-existing unused global suppressions on this base)
• Reconciled with the current active release base release/v3.8.51@158647618; focused checks rerun afterward
• Production-code changes include a new or updated automated test in this PR
• SonarQube is temporarily opt-in while the private project has no quota; it is not a PR gate.

Tests Added Or Updated

• tests/unit/12058-models-catalog-canonical-self-aliased.test.ts (new): antigravity and agy static rows in canonical mode; a self-aliased built-in's synced, custom and alias-backed rows; a normally-aliased control (cc/ vs claude/) proving dual/alias counts are unchanged.

Coverage Notes

• All four touched branches in src/app/api/v1/models/catalog.ts are exercised by the new file; the synced-audio sub-branch was deliberately left unchanged because its mutant survived (that row comes from the primary synced push).

Reviewer Notes

• Behaviour change: canonical mode now lists every active self-aliased provider (previously omitted, and documented as such in API_REFERENCE.md, ENVIRONMENT.md and .env.example; those docs are updated here).
• The issue scoped the ask to the static loop; the same drop was reproduced for built-in providers in the synced, custom and alias-backed loops, so all four are covered to avoid a second round-trip. If a narrower change is preferred, the three non-static sites are single-line reverts with their own assertions to drop.
• The pre-commit hook also Prettier-formatted catalog.ts:925-933 (pre-existing formatting debt).