feat(notion): Finalize relational DB implementation and scripts

- Implement relational data structure in Notion as per the plan.
- Add scripts for initial data import (import_product.py) and distribution to related databases (distribute_product_data.py).
- Create helper scripts for reading Notion content.
- Update Notion_Dashboard.md and GEMINI.md with the latest implementation status, database IDs, and key lessons learned from the MVP phase, including API constraints and schema-first principles.

GEMINI.md

@@ -60,6 +60,18 @@ The system architecture has evolved from a CLI-based toolset to a modern web app
     *   **Problem:** Users didn't see when a background job finished.
     *   **Solution:** Implementing a polling mechanism (`setInterval`) tied to a `isProcessing` state is superior to static timeouts for long-running AI tasks.
 
+6.  **Notion API - Schema First:**
+    *   **Problem:** Scripts failed when trying to write data to a Notion database property (column) that did not exist.
+    *   **Solution:** ALWAYS ensure the database schema is correct *before* attempting to import or update data. Use the `databases.update` endpoint to add the required properties (e.g., "Key Features", "Constraints") programmatically as a preliminary step. The API will not create them on the fly.
+
+7.  **Notion API - Character Limits:**
+    *   **Problem:** API calls failed with a `400 Bad Request` error when a rich text field exceeded the maximum length.
+    *   **Solution:** Be aware of the **2000-character limit** for rich text properties. Implement logic to truncate text content before sending the payload to the Notion API to prevent validation errors.
+
+8.  **Notion API - Response Structures:**
+    *   **Problem:** Parsing functions failed with `TypeError` or `AttributeError` because the JSON structure for a property differed depending on how it was requested.
+    *   **Solution:** Write robust helper functions that can handle multiple possible JSON structures. A property object retrieved via a direct property endpoint (`/pages/{id}/properties/{prop_id}`) is structured differently from the same property when it's part of a full page object (`/pages/{id}`). The parsing logic must account for these variations.
+
 ## Next Steps
 *   **Quality Assurance:** Implement a dedicated "Review Mode" to validate high-potential leads.
 *   **Export:** Generate Excel/CSV enriched reports.