Adds an optional date parameter to journal_new that overrides the
timestamp on new entries. Accepts YYYY-MM-DD or YYYY-MM-DDTHH:MM
format. Used for seeding the memory graph with historical journal
entries from existing memory files.
Threading: CLI --date flag → cmd_journal_write → journal_new tool →
local store, with parse_date_to_epoch setting both timestamp and
created_at on the node.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>