fix: resolve all ruff lint errors and type checker warnings

- Use Annotated[str, Form()] for FastAPI dependencies (FAST002)
- Add missing type annotations across src/ and tests/ (ANN001/003/201/202)
- Reduce function arguments via request.form() reads (PLR0913)
- Combine return paths to reduce return statements (PLR0911)
- Use anyio.Path for async-safe filesystem operations (ASYNC240)
- Extract constants, helpers, and dict comprehensions for clarity
- Move inline imports to top-level (PLC0415)
- Use raw strings for regex match patterns (RUF043)
- Fix redundant get_session_user call in delete_user (not-iterable)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_oidc/test_provider.py

@@ -2,6 +2,7 @@ import shutil
 from pathlib import Path
 
 from porchlight.config import Settings
+from porchlight.oidc.claims import PorchlightUserInfo
 from porchlight.oidc.provider import create_oidc_server
 
 
@@ -49,8 +50,6 @@ def test_create_server_userinfo_is_porchlight() -> None:
     try:
         settings = Settings(issuer="http://localhost:8000", sqlite_path=":memory:", signing_key_path=str(key_path))
         server = create_oidc_server(settings)
-        from porchlight.oidc.claims import PorchlightUserInfo
-
         assert isinstance(server.context.userinfo, PorchlightUserInfo)
     finally:
         shutil.rmtree(key_path, ignore_errors=True)