Give the tests their own database and drop the template specs

pytest was deleting every user on teardown against the development
database. The engine is built at import time, so tests/__init__.py pins
POSTGRES_DB before app.core.config loads; the fixture creates the schema
and drops the database again, guarded against a name that is not _test.

Playwright now defaults at the integrated stack, which is the origin the
API allows, so a bare `bunx playwright test` works without a dev server.
The four template specs that asserted copy we no longer ship are gone,
along with the helpers they were the last callers of. The admin edit
assertion was page-wide and only ever passed on a fresh database.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KkmeRiyeYmVZqJVwuyHq9o

backend/tests/__init__.py

@@ -0,0 +1,11 @@
+"""Redirect the suite at its own database.
+
+`app.core.db` builds the engine at import time and several modules bind that
+object, so the name has to be in the environment before anything imports the
+settings. Overriding it here — the first module pytest imports for the
+package — keeps a test run from touching the development data.
+"""
+
+import os
+
+os.environ["POSTGRES_DB"] = "app_test"