Fix: upload page now attaches files to memories via MCP-generated links

The /app/upload page now correctly handles ?memory_id= links generated by the MCP tool get_upload_link. Previously, uploading a file through an MCP-generated link would land the file in storage but leave it unattached — no entry in memory_assets was created, silently breaking every AI-client upload flow that relied on the auto-attach contract. Files uploaded via a ?memory_id= link now attach to the memory through the edge function REST API, matching how the memory detail page attaches files. Legacy ?thought_id= and ?insight_id= links continue to work unchanged.