Adds a shared common-config/contents-page-name constant and
ldb/contents?/get-contents-page, mirroring the existing Library
helpers. Contents already qualifies as an internal page, so the
existing namespace-title split mechanism (e.g. "Contents/Proyectos")
already parents pages under it via :block/parent, coexisting with
Library rather than replacing it as the default root.
Establishes version control for the personal Logseq DB fork before
starting the server-client architecture migration and domain features
described in docs/agent-guide and the approved implementation plan.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>