feat(harness): single-select answers auto-confirm (reviewer_select persists)

F — reviewer_select options may now carry a `decision` payload {type, subject,
detail?, rationale?} plus an optional `advance`. Picking such an option IS the
confirmation: the gate persists it directly (tht decision add) and optionally
advances, with no redundant reviewer_decide/reviewer_confirm follow-up gate.
Options without a payload stay ask-only; back/exit/Other never persist.

Pure logic extracted + exported for unit tests: resolveSelectOutcome (classifies
the response) and decisionAddArgs (shared with reviewer_decide, DRY). Gate JS
suite 33/33 (gate_select_decision.test.js, +5); harness pytest 269 unchanged.

Contract docs updated together: reviewer_select tool description, SKILL.md
(widget summary, disciplines 2-3, Phase-1 single-pick), and the CLAUDE.md gate
note. Live verification (model truly emits reviewer_select+decision, decision in
review_decisions.jsonl, no follow-up gate) deferred to workstream G — it is
model-behavior-dependent.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CLAUDE.md

@@ -59,8 +59,9 @@ frontend (React/SSE) → backend (Fastify) → pi --mode rpc → tht/harness →
   (`backend/data/settings.json`), not a DB.
 
 - **Human-in-the-loop gate contract.** The model proposes; a human reviewer decides at gates
-  via widgets (`reviewer_select` = iterate/no decision; `reviewer_decide` = the choice IS the
-  decision; `reviewer_confirm` = artifact/phase gate). The frontend renders these
+  via widgets (`reviewer_select` = single pick — a chosen option carrying a `decision` payload
+  auto-confirms/persists directly, an option without one only asks; `reviewer_decide` = multiselect,
+  each choice IS a decision; `reviewer_confirm` = artifact/phase gate). The frontend renders these
   widget-descriptors (`src/widgets/` registry) and the live transcript is rebuilt in-memory
   from the SSE stream (`src/store/sessionStore.ts`) — it is not persisted.