feat(row6): a proposal whose approach declared no requirement is unsupported

Stress round 6 validated three falsification arms, and every validated
approach rested only on run-level declarations nobody can attribute to one
approach. declare_requirement now takes a required approach_id (a mandate
id or own-proposal; an unknown id is refused naming the valid ones), and a
ValidatedProposal whose approach has neither a mandate requirement nor a
declaration under its own id becomes validator.Unsupported - a Rejection
subclass carrying the validator's own ruling, reported as `unsupported` in
coverage, the outcome artefact, the settlement and the judge, and never
counted or summed. The rule is active whenever the debate held the
declaration tool, the micro base included; the road and pre-pass paths are
untouched. Declaration quality is not judged, so the rule can be satisfied
by declaring any document the run read.

The v1 gate's row 6 probes pass; its artefact half reads IKKE MÅLT because
stress round 6 predates approach-addressed declarations, and IKKE MÅLT is
never green - it fails the exit code.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/portfolio_optimiser/validator.py

@@ -102,6 +102,30 @@ class Rejection:
     reason: str
 
 
+#: The ONE sentence an unsupported outcome carries. ``rejection_stage`` keys on it, so the judge can
+#: tell this falsifier from the numeric ones without a second copy of the wording.
+UNSUPPORTED_REASON: Final = (
+    "no declared requirement for this approach: the numbers held, but no requirement of the "
+    "knowledge base was declared as binding it"
+)
+
+
+@dataclass(frozen=True)
+class Unsupported(Rejection):
+    """A proposal whose NUMBERS held but whose approach declared no binding requirement (row 6).
+
+    Neither ``validated`` (nothing in the knowledge base was said to support the direction) nor an
+    ordinary rejection (every numeric stage passed). It subclasses ``Rejection`` on purpose: every
+    consumer that asks "is this validated?" with ``isinstance(..., ValidatedProposal)`` answers no
+    without being touched, so it is never counted, summed or carried as a success. The consumers
+    that NAME the status — coverage, the outcome artefact, the settlement, the judge — check for
+    this class first. ``validated`` keeps the validator's own ruling, which is what
+    ``provenance.validator_decision`` mirrors: the validator said yes, and the record says so.
+    """
+
+    validated: ValidatedProposal
+
+
 def _solve_max_feasible(items: list[AffectedItem], fraction: float) -> float:
     """Real CBC solve: maximize total saving subject to a per-item upper bound and a
     global fraction cap. Raises ``CbcUnavailable`` if CBC is genuinely missing."""
@@ -728,6 +752,7 @@ _REJECTION_STAGES: Final = (
     ("stage4-p90", ("exceeds P90 feasible",)),
     ("stage4b-nominal", ("exceeds the nominal feasible",)),
     ("stage5-method-cap", ("method cap",)),
+    ("unsupported", ("no declared requirement for this approach",)),
 )