feat(ask): Phase 3.5a guardrails (classifier + refusal gate + grounding + partial)

신규 파일:
- classifier_service.py: exaone binary classifier (sufficient/insufficient)
  parallel with evidence, circuit breaker, timeout 5s
- refusal_gate.py: multi-signal fusion (score + classifier)
  AND 조건, conservative fallback 3-tier (classifier 부재 시)
- grounding_check.py: strong/weak flag 분리
  strong: fabricated_number + intent_misalignment(important keywords)
  weak: uncited_claim + low_overlap + intent_misalignment(generic)
  re-gate: 2+ strong → refuse, 1 strong → partial
- sentence_splitter.py: regex 기반 (Phase 3.5b KSS 업그레이드)
- classifier.txt: exaone Y+ prompt (calibration examples 포함)
- search_synthesis_partial.txt: partial answer 전용 프롬프트
- 102_ask_events.sql: /ask 관측 테이블 (completeness 3-분리 지표)
- queries.yaml: Phase 3.5 smoke test 평가셋 10개

수정 파일:
- search.py /ask: classifier parallel + refusal gate + grounding re-gate
  + defense_layers 로깅 + AskResponse completeness/aspects/confirmed_items
- config.yaml: classifier model 섹션 (exaone3.5:7.8b GPU Ollama)
- config.py: classifier optional 파싱
- AskAnswer.svelte: 4분기 렌더 (full/partial/insufficient/loading)
- ask.ts: Completeness + ConfirmedItem 타입

P1 실측: exaone ternary 불안정 → binary gate 축소. partial은 grounding이 담당.
토론 9라운드 확정. plan: quiet-meandering-nova.md

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

migrations/102_ask_events.sql

@@ -0,0 +1,26 @@
+-- Phase 3.5a: /ask 호출 관측 테이블
+-- refusal rate 측정, 지표 3 분리 (full/partial/insufficient), defense layer 디버깅
+
+CREATE TABLE IF NOT EXISTS ask_events (
+    id BIGSERIAL PRIMARY KEY,
+    query TEXT NOT NULL,
+    user_id BIGINT REFERENCES users(id),
+    completeness TEXT,               -- full / partial / insufficient
+    synthesis_status TEXT,
+    confidence TEXT,
+    refused BOOLEAN DEFAULT false,
+    classifier_verdict TEXT,          -- sufficient / insufficient / null (skipped)
+    max_rerank_score REAL,
+    aggregate_score REAL,
+    hallucination_flags JSONB DEFAULT '[]',
+    evidence_count INT,
+    citation_count INT,
+    defense_layers JSONB,            -- per-layer flag snapshot (score_gate, classifier, grounding)
+    total_ms INT,
+    created_at TIMESTAMPTZ DEFAULT now()
+);
+
+CREATE INDEX IF NOT EXISTS idx_ask_events_created ON ask_events(created_at);
+CREATE INDEX IF NOT EXISTS idx_ask_events_completeness ON ask_events(completeness);
+
+INSERT INTO schema_migrations (version) VALUES (102);