Add movie/series ratings and watchlist

Builds on the accounts foundation: PUT/DELETE a rating (0.5-10.0) or a
watchlist entry on any movie or series, all scoped to the bearer token's
own user, plus GET /account/ratings|watchlist/{movies,series} to list
them back. Both are polymorphic entity_type/entity_id tables, same shape
as watch_provider_offerings and trending_entries, so movie and series
share one repository/router each rather than duplicating per type.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

app/schemas/account.py

@@ -0,0 +1,21 @@
+"""Request/response schemas for the authenticated user's own ratings and
+watchlist (section 17, additive)."""
+
+from __future__ import annotations
+
+from datetime import datetime
+
+from pydantic import BaseModel, Field
+
+
+class RatingIn(BaseModel):
+    # 0.5-10.0 in practice (TMDb's own scale), enforced as a continuous
+    # range rather than an enum of 0.5 steps -- not worth the extra
+    # validation for a value nothing downstream treats as discrete.
+    value: float = Field(ge=0.5, le=10.0)
+
+
+class RatingOut(BaseModel):
+    value: float
+    created_at: datetime
+    updated_at: datetime