score: a refuting leaf pack is told to add structured fields it already has

[explosivebit]

Found immediately after v0.37.0 shipped, while re-scoring the graph with the new binary. Introduced by the leaf-EVID scoring work in that release (#325), so this is fresh, not inherited.

Reproducer

```
$ forgeplan score EVID-146

EVID-146 — PROB-078 refuted: MCP read-after-write correct across 7 tests incl real-binary subprocess
Leaf evidence — scored on its own structured fields. R_eff = 0.00

✗ Structured fields missing or undeclared
→ forgeplan get EVID-146 — add verdict: and congruence_level: under ## Structured Fields

• Leaf evidence scored on its own fields: Refutes CL3 = 0.00
```

The output contradicts itself two lines apart. The hint says the structured fields are missing; the factor line below it reports having read them (Refutes CL3). They are present:

```

Structured Fields

verdict: refutes
congruence_level: 3
evidence_type: test
```

Cause

crates/forgeplan-cli/src/commands/score.rs:324 gates the hint on the score alone:

```rust
if report.r_eff <= 0.1 {
ui::error_hint("Structured fields missing or undeclared", ...)
```

That conflates two different reasons for a low leaf score:

• fields absent → CL0 → 0.1. The hint is correct and useful.
• verdict: refutes → 0.00 by design. The fields are present and correct; a refuting pack should score zero. The hint is wrong, and it asks the author to add something already there.

Why it matters more than a cosmetic wording bug

The scoring is right — only the advice is wrong. But following it leads nowhere: you open the file, the fields are there, and the tool keeps saying they aren't. That is the same shape as the defects v0.37.0 was about — a surface reporting something that is not true — and it now lives inside the fix for one of them.

Fix direction

Gate the hint on why the score is low, not on the number. The scorer already knows: it distinguishes Refutes CL3 = 0.00 from a CL0 fallback in the factor it emits. A refuting pack at 0.00 needs no hint at all, or a different one explaining that a refutation scoring zero is the intended reading.

Test that would catch it

Assert on the hint text for a leaf pack with verdict: refutes + congruence_level: 3 — not just on its score. The score was already correct; only the advice regressed, so a score-only assertion passes over this.

Refs: #325, PRD-086, v0.37.0