fix: exclude account_id and virtual fields from archive_content DB writes

- Adds fields_to_exclude_from_db to Archive_Content_Base to prevent SQL errors on non-existent columns.
- Updates documentation for V3 Create/Update patterns and the x-ae-ignore-extra-fields header.
- Propagates account_id_random to hosted file and media processing methods.

documentation/GUIDE__V3_FRONTEND_API.md

@@ -58,6 +58,16 @@ The primary way to retrieve data.
 *   **Endpoint:** `POST /v3/crud/{obj_type}/search`
 *   **Security:** Automatically filters results to only show records belonging to your `x-account-id`. If no account context is provided, it will return **0 records** for private objects.
 
+### C. POST Create / PATCH Update
+Modify data in the system.
+*   **Endpoints:** 
+    *   `POST /v3/crud/{obj_type}/`
+    *   `PATCH /v3/crud/{obj_type}/{id}`
+*   **Strict Mode (Default):** The API validates your payload against the Pydantic model. If you send fields that do not exist in the model, the database might return a 400 "Unknown column" error.
+*   **Permissive Mode (Header):** To allow the frontend to send "extra" fields (like local UI state) without causing errors, use the following header:
+    *   **Header:** `x-ae-ignore-extra-fields: true`
+    *   **Behavior:** When set to `true`, the backend will automatically strip any fields from the payload that are not defined in the object's model before attempting to save to the database.
+
 ---
 
 ## 4. V3 Uniform Lookup System