fix(briefing): split migration into 4 single-statement files

asyncpg 의 prepared statement 가 multi-statement 불허. Phase 4 101 SQL 은
2026-04-08 적용 당시엔 통과했지만 현재 asyncpg/sqlalchemy 버전에서 fail.

255_morning_briefings_table.sql  CREATE TABLE morning_briefings
256_morning_briefings_idx.sql    CREATE INDEX (briefing_date)
257_briefing_topics_table.sql    CREATE TABLE briefing_topics + UNIQUE
258_briefing_topics_idx.sql      CREATE INDEX (briefing_id, topic_rank)

migrations/255_morning_briefings.sql

@@ -1,50 +0,0 @@
--- 야간 수집 뉴스 브리핑 (Morning Briefing)
--- 매일 KST 자정~05:00 사이 수집된 뉴스를 topic-country 비교 분석 1페이지 카드.
--- 트리거: 05:10 KST APScheduler cron (PR-3 에서 등록). Phase 4 와 axis 반대 (topic-first).
--- 코드/로직/테이블 모두 Phase 4 와 분리. 공통 알고리즘만 services/clustering_common 공유.
-
-CREATE TABLE morning_briefings (
-    id                BIGSERIAL PRIMARY KEY,
-    briefing_date     DATE NOT NULL,
-    window_start      TIMESTAMPTZ NOT NULL,
-    window_end        TIMESTAMPTZ NOT NULL,
-    decay_lambda      DOUBLE PRECISION NOT NULL,
-    total_articles    INTEGER NOT NULL DEFAULT 0,
-    total_countries   INTEGER NOT NULL DEFAULT 0,
-    total_topics      INTEGER NOT NULL DEFAULT 0,
-    generation_ms     INTEGER,
-    llm_calls         INTEGER NOT NULL DEFAULT 0,
-    llm_failures      INTEGER NOT NULL DEFAULT 0,
-    status            VARCHAR(20) NOT NULL DEFAULT 'success',
-    headline_oneliner TEXT,
-    created_at        TIMESTAMPTZ NOT NULL DEFAULT NOW(),
-    UNIQUE (briefing_date)
-);
-
-CREATE INDEX idx_morning_briefings_date ON morning_briefings (briefing_date DESC);
-
-CREATE TABLE briefing_topics (
-    id                     BIGSERIAL PRIMARY KEY,
-    briefing_id            BIGINT NOT NULL REFERENCES morning_briefings(id) ON DELETE CASCADE,
-    topic_rank             INTEGER NOT NULL,
-    topic_label            VARCHAR(120) NOT NULL,
-    headline               TEXT NOT NULL,
-    country_perspectives   JSONB NOT NULL DEFAULT '[]',
-    divergences            JSONB NOT NULL DEFAULT '[]',
-    convergences           JSONB NOT NULL DEFAULT '[]',
-    key_quotes             JSONB NOT NULL DEFAULT '[]',
-    historical_article_ids JSONB,
-    historical_context     TEXT,
-    historical_window_days INTEGER,
-    cluster_members        JSONB NOT NULL DEFAULT '[]',
-    article_count          INTEGER NOT NULL,
-    country_count          INTEGER NOT NULL,
-    importance_score       DOUBLE PRECISION NOT NULL,
-    raw_weight_sum         DOUBLE PRECISION NOT NULL,
-    llm_model              VARCHAR(100),
-    llm_fallback_used      BOOLEAN NOT NULL DEFAULT FALSE,
-    created_at             TIMESTAMPTZ NOT NULL DEFAULT NOW(),
-    UNIQUE (briefing_id, topic_rank)
-);
-
-CREATE INDEX idx_briefing_topics_briefing_rank ON briefing_topics (briefing_id, topic_rank);

migrations/255_morning_briefings_table.sql

@@ -0,0 +1,19 @@
+-- Morning Briefing 부모 테이블 (일일 1행, briefing_date UNIQUE).
+-- asyncpg prepared statement 가 multi-statement 불허라 인덱스 + 자식 테이블은 별 migration.
+CREATE TABLE morning_briefings (
+    id                BIGSERIAL PRIMARY KEY,
+    briefing_date     DATE NOT NULL,
+    window_start      TIMESTAMPTZ NOT NULL,
+    window_end        TIMESTAMPTZ NOT NULL,
+    decay_lambda      DOUBLE PRECISION NOT NULL,
+    total_articles    INTEGER NOT NULL DEFAULT 0,
+    total_countries   INTEGER NOT NULL DEFAULT 0,
+    total_topics      INTEGER NOT NULL DEFAULT 0,
+    generation_ms     INTEGER,
+    llm_calls         INTEGER NOT NULL DEFAULT 0,
+    llm_failures      INTEGER NOT NULL DEFAULT 0,
+    status            VARCHAR(20) NOT NULL DEFAULT 'success',
+    headline_oneliner TEXT,
+    created_at        TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    UNIQUE (briefing_date)
+)

migrations/256_morning_briefings_idx.sql

@@ -0,0 +1 @@
+CREATE INDEX idx_morning_briefings_date ON morning_briefings (briefing_date DESC)

migrations/257_briefing_topics_table.sql

@@ -0,0 +1,26 @@
+-- Morning Briefing 자식 (topic_rank 순, UNIQUE briefing_id + topic_rank).
+-- country_perspectives/divergences/convergences/key_quotes JSONB (cap 은 application).
+-- historical_* 3 컬럼은 BRIEFING_HISTORICAL_ENABLED on 시만 채움 (nullable).
+CREATE TABLE briefing_topics (
+    id                     BIGSERIAL PRIMARY KEY,
+    briefing_id            BIGINT NOT NULL REFERENCES morning_briefings(id) ON DELETE CASCADE,
+    topic_rank             INTEGER NOT NULL,
+    topic_label            VARCHAR(120) NOT NULL,
+    headline               TEXT NOT NULL,
+    country_perspectives   JSONB NOT NULL DEFAULT '[]',
+    divergences            JSONB NOT NULL DEFAULT '[]',
+    convergences           JSONB NOT NULL DEFAULT '[]',
+    key_quotes             JSONB NOT NULL DEFAULT '[]',
+    historical_article_ids JSONB,
+    historical_context     TEXT,
+    historical_window_days INTEGER,
+    cluster_members        JSONB NOT NULL DEFAULT '[]',
+    article_count          INTEGER NOT NULL,
+    country_count          INTEGER NOT NULL,
+    importance_score       DOUBLE PRECISION NOT NULL,
+    raw_weight_sum         DOUBLE PRECISION NOT NULL,
+    llm_model              VARCHAR(100),
+    llm_fallback_used      BOOLEAN NOT NULL DEFAULT FALSE,
+    created_at             TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    UNIQUE (briefing_id, topic_rank)
+)

migrations/258_briefing_topics_idx.sql

@@ -0,0 +1 @@
+CREATE INDEX idx_briefing_topics_briefing_rank ON briefing_topics (briefing_id, topic_rank)