fix: a self-contradicting test fixture, and import order (E4 follow-up)

Two failures on 51e78a3, neither in the shipped logic.

**The integration failure was a TEST bug, not a code bug.**
`test_a_weak_name_needs_the_declaration` set `display_name` to something
deliberately weak but left `_membership`'s DEFAULT vanity, which matched the
artist slug exactly. So the name signal was legitimately 1.0 and the matcher
was right to propose — my assertion of 0 was asserting the wrong scenario.
Both identity fields now have to be weak for the test to mean what it says,
and the arithmetic was checked before pushing: 0.39 without the declaration,
0.74 with it.

Worth keeping: a fixture whose fields disagree with each other will pass or
fail for reasons unrelated to the property under test, and this one was one
default away from silently testing nothing.

**The lint failure was import order** — `artist_membership_service` sorts
before `credential_*` and I inserted it after. Second isort slip this session
from patching an import block with a script rather than reading it back; the
repo has a rule about exactly this (#102).

Everything else passed on that SHA: 1256 tests, the frontend suite, and
migration 0096.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LNXXULQDjVZmbuNa2G9mD9

backend/app/tasks/maintenance.py

@@ -1244,9 +1244,9 @@ def sync_memberships() -> str:
     """
     import asyncio
 
+    from ..services.artist_membership_service import rescan as membership_rescan
     from ..services.credential_crypto import CredentialCrypto
     from ..services.credential_service import CredentialService
-    from ..services.artist_membership_service import rescan as membership_rescan
     from ..services.membership_roster import sync_platform
     from ..services.patreon_client import PatreonClient
     from ._async_session import async_session_factory

tests/test_artist_membership_suggestions.py

@@ -181,13 +181,21 @@ async def test_an_artist_with_no_sources_at_all_is_never_proposed(db):
 @pytest.mark.asyncio
 async def test_a_weak_name_needs_the_declaration(db):
     artist = await _artist_with_discord(db, "Maewix", "maewix")
-    m = await _membership(db, display_name="Maewix Studios Official")
+    # BOTH identity fields must be weak, or the test contradicts itself: the
+    # first draft left the default vanity exactly matching the artist slug, so
+    # the name signal was legitimately 1.0 and the code was right to propose.
+    # CI caught it — a test bug, not a code bug.
+    m = await _membership(
+        db, display_name="Maewix Studios Official",
+        details={"campaign": {"vanity": "maewixstudios"}},
+        url="https://www.patreon.com/maewixstudios",
+    )
     await db.commit()
     assert await ArtistMembershipService(db).match_membership(m.id) == 0
 
     db.add(Post(
         artist_id=artist.id, source_id=None, external_post_id="p1",
-        description='<a href="https://www.patreon.com/maewix">my patreon</a>',
+        description='<a href="https://www.patreon.com/maewixstudios">mine</a>',
         post_date=datetime.now(UTC),
     ))
     await db.commit()