Previously a single "that name or URL" message was thrown regardless of which
column violated uniqueness. Now the catch block inspects the error string from
SQLite to emit a name-specific or url-specific message, with a generic fallback
when neither column can be identified.
Adds vitest tests covering all four scenarios: name conflict, url conflict,
unknown column conflict, and non-UNIQUE error passthrough.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
