feat(persona): build the shared expert-reviewer persona as a framework-neutral Agent Skill

The expert reviewer was only a hardcoded verdict_input dict inside the offline
simulation. Build it as the real, shared artifact target picture §8 calls for:
shared/skills/expert-reviewer/ — a SKILL.md persona prompt (energy-advisor / M&V
role + the realization-gap methodology the validator cannot compute) plus a
canonical references/example-verdict.json. shared/ stays pure data; the MAF side
reads it via portfolio_optimiser.persona.load_persona_example (call-time,
fail-fast) and the Claude-SDK sibling reads the same JSON with its own loader.

This de-stubs the simulation: its persona judgement (decision + rationale + traced
marker) is now sourced from the artifact at call time, not an inline literal — so
the shared persona is genuinely consumed and cannot rot silently. decision is
binary (approved/rejected, the FeedbackContract the run path accepts);
approved_with_adjustment is rejected there and lives only in the bundle seed
frontmatter + the promotion gate, so the realization correction is carried in the
rationale prose.

Load-bearing trio (tests/test_persona_skill_loadbearing.py), each proven RED on its
own detach: structure + framework-neutrality, the example is valid pipeline input
(incl. FeedbackContract, on a throwaway copy), and the simulation's marker follows
the artifact file. Suite 149->152.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MHR8iKxJRxDiDfNw8HZmWE

src/portfolio_optimiser/persona.py

@@ -0,0 +1,52 @@
+"""Loader for the shared expert-reviewer persona artifact (målbilde §8).
+
+The persona lives in ``shared/skills/expert-reviewer/`` as a framework-neutral Agent Skill (SKILL.md
++ a canonical example verdict). ``shared/`` stays pure DATA — this loader is the MAF-side reader of
+it; the Claude-SDK sibling reads the same JSON with its own loader. This is what de-stubs the
+offline simulation: its persona judgement is sourced from the artifact instead of a hardcoded
+literal, so the shared persona is genuinely consumed (and cannot rot silently).
+
+Fail-fast on purpose: the example is REQUIRED input (contrast the tolerant async verdict inbox,
+``verdicts.load_verdicts_from_dir``). A missing or malformed file raises rather than degrading —
+a broken shared artifact must surface, not pass silently.
+"""
+
+from __future__ import annotations
+
+import json
+from dataclasses import dataclass
+from pathlib import Path
+
+# Module-global so tests can monkeypatch it; read at CALL time inside the loader (never frozen into
+# a default argument), which is what makes the simulation's persona genuinely artifact-driven.
+_EXAMPLE_PATH = (
+    Path(__file__).resolve().parents[2]
+    / "shared"
+    / "skills"
+    / "expert-reviewer"
+    / "references"
+    / "example-verdict.json"
+)
+
+
+@dataclass(frozen=True)
+class PersonaExample:
+    """The expert-reviewer persona's canonical example verdict: the judgement the persona renders for
+    the reference measure. ``marker`` is a substring of ``rationale`` (the realization-rate payload
+    the simulation traces across runs)."""
+
+    decision: str
+    rationale: str
+    marker: str
+
+
+def load_persona_example() -> PersonaExample:
+    """Read the persona's canonical example verdict. Fail-fast: a missing file raises
+    ``FileNotFoundError`` and a missing key raises ``KeyError`` (required input). Reads
+    ``_EXAMPLE_PATH`` at call time so the path is patchable."""
+    data = json.loads(_EXAMPLE_PATH.read_text(encoding="utf-8"))
+    return PersonaExample(
+        decision=data["decision"],
+        rationale=data["rationale"],
+        marker=data["marker"],
+    )