docs: correct the v2 filter allowlist, date operators, and OSS operator scope

Probing production surfaced three more inaccuracies:

- the allowlist row listed 'text' and 'keywords_search', which only exist on
  the search endpoint, and omitted the get_all-only fields
- the time-field table listed 'eq', which every date field rejects with a 400,
  and omitted 'expiration_date' entirely
- the nested AND/OR example filtered categories with a bare string, which the
  API rejects with "'categories' value must be a dictionary"

Also scoped the OSS operator claim to the filter layer: Chroma falls back to
equality for contains/icontains and Pinecone maps neither.

docs/platform/features/v2-memory-filters.mdx

@@ -42,9 +42,10 @@ Filters use a nested JSON structure with logical operators at the root:
 ### Time fields
 | Field | Operators | Example |
 |-------|-----------|---------|
-| `created_at` | `gt`, `gte`, `lt`, `lte`, `eq`, `ne` | `{"created_at": {"gte": "2024-01-01"}}` |
-| `updated_at` | `gt`, `gte`, `lt`, `lte`, `eq`, `ne` | `{"updated_at": {"lt": "2024-12-31"}}` |
-| `timestamp` | `gt`, `gte`, `lt`, `lte`, `eq`, `ne` | `{"timestamp": {"gt": "2024-01-01"}}` |
+| `created_at` | `gt`, `gte`, `lt`, `lte`, `ne`, `in`. Explicit `eq` is rejected, pass a bare value instead | `{"created_at": {"gte": "2024-01-01"}}` |
+| `updated_at` | `gt`, `gte`, `lt`, `lte`, `ne`, `in`. Explicit `eq` is rejected, pass a bare value instead | `{"updated_at": {"lt": "2024-12-31"}}` |
+| `timestamp` | `gt`, `gte`, `lt`, `lte`, `ne`, `in`. Explicit `eq` is rejected, pass a bare value instead | `{"timestamp": {"gt": "2024-01-01"}}` |
+| `expiration_date` | `gt`, `gte`, `lt`, `lte`, `ne`, `in`. Explicit `eq` is rejected, pass a bare value instead | `{"expiration_date": {"lte": "2026-12-31"}}` |
 
 ### Content fields
 | Field | Operators | Example |
@@ -421,8 +422,8 @@ A filter object with both an `AND` key and a sibling `OR` key at the same level
         "AND": [
             {"user_id": "user_123"},
             {"OR": [
-                {"categories": "finance"},
-                {"categories": "health"}
+                {"categories": {"in": ["finance"]}},
+                {"categories": {"in": ["health"]}}
             ]}
         ]
     }