fix(codegen): preserve regenerated response aliases

[sangilish]

Summary

Refs #822.

This rebuilds the codegen response-alias fix on current main after the earlier branch conflicted with the AdCP 3.1 generated/type-codegen changes.

The change keeps the clean-regeneration path working for restored response aliases:

• re-sync ProtocolEnvelope imports after post_generate_fixes.py restores manual response arms
• include annotated TypeAlias assignments when consolidating generated exports
• avoid eager _g.FooResponse fallback lookups in aliases.py
• commit the regenerated type outputs from the fixed pipeline
• add regression coverage for those three failure modes

Testing

• uv run --extra dev python scripts/generate_types.py
• uv run --extra dev python -c "from adcp.types import _generated; from adcp.types import aliases; print('import-ok')"
• uv run --extra dev pytest tests/test_code_generation.py tests/test_asset_aliases_stable.py tests/test_schemas_version_pin.py -q --tb=short
• uv run --extra dev ruff check --ignore E501 scripts/consolidate_exports.py scripts/post_generate_fixes.py src/adcp/types/aliases.py tests/test_code_generation.py
• git diff --check

Full-suite note: uv run --extra dev pytest -q --tb=short completed with one unrelated wall-clock boundary failure in tests/test_pg_idempotency_backend.py::test_delete_expired_defaults_to_wall_clock (5277 passed, 38 skipped, 9 deselected, 1 xfailed, 1 failed). Re-running that single test passed: uv run --extra dev pytest tests/test_pg_idempotency_backend.py::test_delete_expired_defaults_to_wall_clock -q --tb=short.

[bokelley]

Tried to update this branch against current main, but GitHub reports conflicts. I confirmed the conflicts are in generated/type-codegen areas touched since this branch was cut: scripts/post_generate_fixes.py, scripts/consolidate_exports.py, src/adcp/types/_generated.py, src/adcp/types/aliases.py, and media-buy generated POC response modules that now include the AdCP 3.1 task-envelope/media_buy_status changes. Moving this out of the review-ready bucket until it is rebased/regenerated on current main.

[bokelley]

Reviewed local follow-up changes; checks are green.

[bokelley]

Reviewed latest follow-up changes; CI is green.

[bokelley]

Closed as superseded by #854, which carried the same patch stack on an in-repository branch so CodeQL and Argus could run under normal branch protection.