testsuite: add COVERAGE.md matrix and -u/--force coverage

testsuite: add COVERAGE.md matrix and -u/--force coverage

COVERAGE.md is the living checklist mapping every CLI option (~142) and daemon
parameter (~54) to its test(s), with depth / cross-dir status and remaining
gaps, so the path-resolution restructure can see exactly what is guarded.

update_test.py closes two of the documented gaps: -u/--update (keep a newer
destination, update an older one) and --force (replace a non-empty destination
directory with a file), both at depth.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>