User-scoped dashboard route tests set a session cookie for a synthetic user but
only stubbed the database in the route-handler modules — not the one the auth
middleware consults. The middleware's "account deleted" guard
(get_user_by_id(user_id) is falsy -> redirect to /dashboard/login) therefore
bounced every request until httpx raised TooManyRedirects, failing ~32 tests.

Add tests/routes/conftest.py with an autouse fixture that wraps
DatabaseRegistry.get_config_database so get_user_by_id returns a present user
ONLY when the lookup comes from the auth middleware (detected via call stack).
Direct database assertions in other tests (e.g. signup cleanup, which expects
deleted users to read back as None) keep observing the real database, and tests
that install their own get_config_database stub still win.

Route suite: TooManyRedirects failures 32 -> 0. Remaining route failures are
unrelated pre-existing issues (studio tests await-ing coroutines, a handler
awaiting a dict, a stub missing record_dashboard_event, template bootstrap
content drift) and are out of scope for this fix.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>