chore(m176): close — spec to done, 32 dimensions graded from green lanes

`orly gate pr` reported 7 of 32 dimensions not DONE. The work was done; the
BOOKKEEPING was not, and four of the seven were carrying test names invented at
planning time that no suite ever used:

    5.1  test_route_meta_total       -> test_every_route_is_walked_exactly_once
    5.3  test_header_limit_16k       -> test_a_head_just_inside_the_allowance_is_served
                                        test_a_head_past_the_allowance_is_refused
    5.4  test_problem_json_envelope  -> test_the_base_envelope_is_the_five_fields_and_no_others
    5.5  test_credential_directories -> test_an_unmatched_digest_is_none_not_an_error
                                        test_a_refused_statement_is_unavailable_not_unknown

Each now names the function that actually exists and the file it lives in, so
the Test column is something a reader can grep rather than a name from before
the code did. 5.2, 6.1 and 6.2 already named their tests correctly and only
lacked the marker. The Test Specification table carried the same three stale
names and is corrected with them.

A spec whose Test column does not resolve is worse than one with no column: it
reads as a claim that something was verified, and the grep that would check it
comes back empty.

Spec moves to done/, which is the step the gate names as CHORE(close).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>