Fix spec creation failing on long text fields

Spec creation (and other writes) longer than 255 characters failed with a string_data_right_truncation error and surfaced to MCP clients as an unresponsive server. The specs.summary, projects.description, drops.title, and drops.external_id columns have been widened from varchar(255) to text, so values up to their validated maximums (280 or 500 characters) now persist successfully.