Backend tests run on SQLite by default (78 passed, 1 skipped); no Postgres needed

- conftest: default SHONAR_TEST_DATABASE_URL is a temp SQLite file, matching
  the bundled-lite engine; set the env var to a PG URL to exercise that path
- models.py: add sqlite_where to the two partial unique indexes — without it
  SQLite built a FULL unique index on recording_id (WHERE not carried over),
  wrongly blocking a second export asset per recording
- test_m9: pass UUID objects (not str) to direct ORM inserts/gets; SQLite's
  GUID bind processor rejects strings (asyncpg tolerated them)

Verified: pytest -q = 78 passed, 1 skipped; ruff check clean

backend/tests/test_m9.py

@@ -7,6 +7,7 @@ via SHONAR_TEST_DATABASE_URL) — both paths share the endpoint contract.
 from __future__ import annotations
 
 import io
+import uuid
 import zipfile
 
 from tests.test_recordings import auth, user_tokens, wav_bytes
@@ -44,7 +45,15 @@ async def add_transcript(rec_id: str, text: str, segments=None):
     from shonar.db.session import session_factory
 
     async with session_factory()() as s:
-        s.add(Transcript(recording_id=rec_id, text=text, segments=segments, provider="test"))
+        # UUID object (not str): SQLite's GUID bind processor requires it.
+        s.add(
+            Transcript(
+                recording_id=uuid.UUID(rec_id) if isinstance(rec_id, str) else rec_id,
+                text=text,
+                segments=segments,
+                provider="test",
+            )
+        )
         await s.commit()
 
 
@@ -53,7 +62,13 @@ async def add_summary(rec_id: str, content: dict):
     from shonar.db.session import session_factory
 
     async with session_factory()() as s:
-        s.add(Summary(recording_id=rec_id, content=content, provider="test"))
+        s.add(
+            Summary(
+                recording_id=uuid.UUID(rec_id) if isinstance(rec_id, str) else rec_id,
+                content=content,
+                provider="test",
+            )
+        )
         await s.commit()
 
 
@@ -241,7 +256,7 @@ async def test_retention_sweep_purges_expired(client):
     r = await client.delete(f"/api/v1/recordings/{rid}", headers=h)
     assert r.status_code == 204
     async with session_factory()() as s:
-        rec = await s.get(Recording, rid)
+        rec = await s.get(Recording, uuid.UUID(rid))
         rec.deleted_at = utcnow() - timedelta(days=31)
         # remember the storage key before the row vanishes
         from shonar.db.models import Asset
@@ -260,7 +275,7 @@ async def test_retention_sweep_purges_expired(client):
     assert purged["files"] >= 1
 
     async with session_factory()() as s:
-        assert await s.get(Recording, rid) is None
+        assert await s.get(Recording, uuid.UUID(rid)) is None
     from shonar.storage import get_storage
 
     assert not await get_storage().exists(storage_key)  # file gone too
@@ -271,7 +286,7 @@ async def test_retention_sweep_purges_expired(client):
     purged = await retention.sweep_deleted()
     assert purged["recordings"] == 0
     async with session_factory()() as s:
-        assert await s.get(Recording, rid2) is not None
+        assert await s.get(Recording, uuid.UUID(rid2)) is not None
 
 
 async def test_retention_sweep_account(client):
@@ -292,7 +307,7 @@ async def test_retention_sweep_account(client):
     purged = await retention.sweep_deleted()
     assert purged["users"] == 1
     async with session_factory()() as s:
-        assert await s.get(Recording, rid) is None  # cascade
+        assert await s.get(Recording, uuid.UUID(rid)) is None  # cascade
         assert await s.scalar(select_user("m9r2@example.com")) is None