Phase 8: hard-cut identity auth routes

[earayu]

Summary

Phase 8 task #36: identity/auth route dependency hard-cut.

• Move legacy aperag/views/auth.py into aperag/domains/identity/api/auth_routes.py and delete aperag/auth/*.
• Move auth dependency wiring into aperag/domains/identity/service/auth_dependencies.py and login-method config helpers into aperag/domains/identity/service/login_methods.py.
• Mount identity auth at /api/v2/auth and config at /api/v2/config; remove the old /api/v1 auth/config route exposure.
• Update domain route imports, remaining legacy v1 routes that still consume auth dependencies, FE typed adapters, hurl/e2e scripts, and schema path keys for the auth/config hard-cut.
• Add a modularization boundary test banning domain imports from aperag.views.auth.

Boundary Notes

• Does not change other v1 ghosts: prompts / quota / export / settings / openai / main / collections / chat_documents / test stay for later domain sweeps.
• Does not carve ORM classes. Invitation was carved by task [Features] support chinese model baichuan-13b #39 / PR cleanup(phase8/task39): legacy ORM carve + old evaluation stack hard-delete + partial unique indexes #1670, then this PR rebased onto main@6bcc0ef2 and now imports Invitation directly from aperag.domains.identity.db.models.
• The temporary runtime bridge from the earlier review head is removed; there is no static domain -> legacy aggregate import.

Verification

• uv run pytest tests/unit_test/test_modularization_boundaries.py tests/unit_test/test_openapi_spec.py -q -> 24 passed
• uv run pytest tests/unit_test/test_web_typed_api_contract.py::test_final_sweep_v1_ghost_paths_are_gone_from_exported_spec tests/unit_test/test_web_typed_api_contract.py::test_e2e_http_does_not_call_removed_v1_paths tests/unit_test/test_web_typed_api_contract.py::test_phase1_fe_complete_identity_auth_admin_audit_adapter_boundary -q -> 3 passed
• uv run python scripts/export_openapi.py --check -> pass
• uv run ruff check aperag tests/unit_test/test_modularization_boundaries.py tests/unit_test/test_openapi_spec.py tests/unit_test/test_web_typed_api_contract.py tests/e2e_pytest/conftest.py -> pass
• cd web && yarn lint -> pass
• git diff --check origin/main...HEAD -> pass
• route smoke via aperag.app: /api/v2/auth/{login,register,user,users,invite,invitations,change-password} and /api/v2/config present; old /api/v1/{login,register,user,users,invite,config} absent

cd web && yarn tsc --noEmit still fails on known mainline FE type issues in page.tsx, collection-form.tsx, chat-input.tsx, and collection-provider.tsx; none are introduced by this PR.