Add missing ND→D report signals and update PR5 completion status

[Copilot]

pr5.txt requested a concrete completion percentage and continued work on the ND→D loop-splice system. This PR advances that work by closing reporting gaps in the classifier/converter and recording updated completion progress in the requirements file.

• ND classifier report coverage

  • Extended nd_classify_program/3 reporting to emit per-predicate MNN signature outcomes:
    • mnn_signature_matched/2
    • mnn_signature_unknown/2
  • Integrated signature-based class selection into clause classification flow.

• Unsafe conversion visibility

  • Updated nd_to_loop_predicate/4 to emit unsafe_nd_conversion/2 when conversion is blocked by unsafe nondeterminism, instead of only generic skip reporting.

• Web UI report parity

  • Updated the MNN Signature Index panel in plop.html to distinguish matched vs unknown signatures in displayed report labels.

• Spec progress update

  • Added an explicit completion update (~92% complete) and remaining gaps to pr5.txt.

% New report signaling in predicate-level ND conversion:
nd_to_loop_predicate(Predicate, ProgramIR, OptimisedIR, Report) :-
    can_convert_1_to_1(Predicate, ProgramIR, Decision),
    (   Decision = no(unsafe_nd(Reasons))
    ->  OptimisedIR = ProgramIR,
        Report = [unsafe_nd_conversion(Predicate, Reasons)]
    ;   ...
    ).