feat(saved-views): scope saved views by module source (backend)

Saved "smart views" were feed-only; the Plex module is getting them too. Add a
`source` discriminator to saved_views ("feed" | "plex"), default "feed" so every
existing row and any source-less client stays feed. Widen the per-user unique
name constraint to (user_id, source, name) so a feed view and a Plex view can
share a name, and scope create's position numbering + the is_default "clear the
others" to (user, source).

Migration 0073 (ADD source NOT NULL server_default 'feed' + swap the unique
constraint; reversible). Endpoints: GET/POST take `source` (default feed).
Tests: source isolation, per-source default, per-source name uniqueness.

backend/app/routes/saved_views.py

@@ -9,11 +9,19 @@ from app.db import get_db
 from app.models import SavedView, User
 from app.routes._common import owned_or_404
 
-# Saved "smart views": per-user named snapshots of the feed's FeedFilters. Gated behind
-# require_human so the shared demo account can't pollute a communal list (mirrors how other
-# personal-state writes are scoped).
+# Saved "smart views": per-user named snapshots of a module's filters (feed or plex, keyed by
+# `source`). Gated behind require_human so the shared demo account can't pollute a communal list
+# (mirrors how other personal-state writes are scoped).
 router = APIRouter(prefix="/api/saved-views", tags=["saved-views"])
 
+# The modules that own saved views. A view is scoped to exactly one; the default is "feed" so a caller
+# (or an older client) that omits `source` keeps the original feed behaviour.
+_SOURCES = {"feed", "plex"}
+
+
+def _norm_source(source: str) -> str:
+    return source if source in _SOURCES else "feed"
+
 
 def _serialize(v: SavedView) -> dict:
     return {
@@ -27,12 +35,15 @@ def _serialize(v: SavedView) -> dict:
 
 @router.get("")
 def list_views(
-    user: User = Depends(require_human), db: Session = Depends(get_db)
+    source: str = "feed",
+    user: User = Depends(require_human),
+    db: Session = Depends(get_db),
 ) -> list[dict]:
+    source = _norm_source(source)
     rows = (
         db.execute(
             select(SavedView)
-            .where(SavedView.user_id == user.id)
+            .where(SavedView.user_id == user.id, SavedView.source == source)
             .order_by(SavedView.position, SavedView.id)
         )
         .scalars()
@@ -44,6 +55,7 @@ def list_views(
 class CreateViewIn(BaseModel):
     name: str
     filters: dict
+    source: str = "feed"
 
 
 @router.post("")
@@ -55,13 +67,19 @@ def create_view(
     name = body.name.strip()
     if not name:
         raise HTTPException(status_code=400, detail="name is required")
+    source = _norm_source(body.source)
+    # Position is per (user, source), so each module's views number 0..N independently.
     maxpos = db.execute(
         select(func.coalesce(func.max(SavedView.position), -1)).where(
-            SavedView.user_id == user.id
+            SavedView.user_id == user.id, SavedView.source == source
         )
     ).scalar_one()
     view = SavedView(
-        user_id=user.id, name=name[:80], filters=body.filters, position=maxpos + 1
+        user_id=user.id,
+        source=source,
+        name=name[:80],
+        filters=body.filters,
+        position=maxpos + 1,
     )
     db.add(view)
     try:
@@ -107,10 +125,14 @@ def update_view(
     if "is_default" in sent:
         make_default = bool(body.is_default)
         if make_default:
-            # At most one default per user: clear the flag on the others first.
+            # At most one default per (user, source): clear the flag on this module's others first.
             db.execute(
                 update(SavedView)
-                .where(SavedView.user_id == user.id, SavedView.id != view.id)
+                .where(
+                    SavedView.user_id == user.id,
+                    SavedView.source == view.source,
+                    SavedView.id != view.id,
+                )
                 .values(is_default=False)
             )
         view.is_default = make_default