archivebox add and other entry points now seed Crawl.urls as
CrawlSeed JSONL at depth=0 (the input layer) with max_depth=depth
for direct URLs and depth+1 only for stdin/import text where the
synthetic archivebox://internal root lives at depth=0. The runner
also accepts one plain URL per line for ORM/crawl-create/schedule
callers so every Crawl row goes through the same expansion path
without scattering CrawlSeed knowledge across the codebase.
Tests updated to match restored convention.
