fix: migrations preserve trend history across reinstalls

Migration 023 was deleting all but the latest trend_windows row per
entity before 024 could save them to trend_history. On reinstall,
this wiped the entire history every time.

Fixed by restructuring:
- 023 now creates trend_history FIRST and copies all trend_windows
  rows into it before deduplicating trend_windows down to latest-only.
  Uses NOT EXISTS to avoid duplicating rows on re-runs.
- 024 is now idempotent: ensures table/indexes exist and backfills
  from recommendations (last 7 days, 1 point per ticker/window/hour)
  to reconstruct approximate history even if trend_windows was sparse.

Both migrations are safe to re-run on existing databases.

infra/migrations/023_trend_windows_upsert_and_cleanup.sql

@@ -1,7 +1,49 @@
 -- Fix trend_windows to upsert instead of accumulating rows.
--- Add unique constraint so ON CONFLICT works, then deduplicate existing data.
+-- First, preserve all historical data in trend_history before deduplicating.
 
--- Step 1: Keep only the most recent row per (entity_type, entity_id, window)
+-- Step 1: Create trend_history table if it doesn't exist yet
+-- (migration 024 also creates it, but we need it here first to preserve data)
+CREATE TABLE IF NOT EXISTS trend_history (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    entity_type VARCHAR(50) NOT NULL DEFAULT 'company',
+    entity_id VARCHAR(100) NOT NULL,
+    "window" VARCHAR(20) NOT NULL,
+    trend_direction VARCHAR(20) NOT NULL DEFAULT 'neutral',
+    trend_strength FLOAT DEFAULT 0.5,
+    confidence FLOAT DEFAULT 0.5,
+    contradiction_score FLOAT DEFAULT 0.0,
+    dominant_catalysts JSONB DEFAULT '[]',
+    material_risks JSONB DEFAULT '[]',
+    generated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_trend_history_lookup
+    ON trend_history (entity_id, "window", generated_at DESC);
+
+CREATE INDEX IF NOT EXISTS idx_trend_history_generated
+    ON trend_history (generated_at DESC);
+
+-- Step 2: Copy ALL existing trend_windows rows into trend_history
+-- before we delete any. This preserves the full history for charting.
+INSERT INTO trend_history (
+    entity_type, entity_id, "window", trend_direction,
+    trend_strength, confidence, contradiction_score,
+    dominant_catalysts, material_risks, generated_at
+)
+SELECT
+    entity_type, entity_id, "window", trend_direction,
+    trend_strength, confidence, contradiction_score,
+    dominant_catalysts, material_risks, generated_at
+FROM trend_windows
+WHERE NOT EXISTS (
+    SELECT 1 FROM trend_history th
+    WHERE th.entity_id = trend_windows.entity_id
+      AND th."window" = trend_windows."window"
+      AND th.generated_at = trend_windows.generated_at
+);
+
+-- Step 3: Keep only the most recent row per (entity_type, entity_id, window)
+-- in trend_windows (it becomes the "latest snapshot" table)
 DELETE FROM trend_windows
 WHERE id NOT IN (
     SELECT DISTINCT ON (entity_type, entity_id, "window") id
@@ -9,15 +51,15 @@ WHERE id NOT IN (
     ORDER BY entity_type, entity_id, "window", generated_at DESC
 );
 
--- Step 2: Add unique constraint for upsert
+-- Step 4: Add unique constraint for upsert
 CREATE UNIQUE INDEX IF NOT EXISTS idx_trend_windows_entity_window
     ON trend_windows (entity_type, entity_id, "window");
 
--- Step 3: Clean up old competitive signal records (keep last 30 days)
+-- Step 5: Clean up old competitive signal records (keep last 30 days)
 DELETE FROM competitive_signal_records
 WHERE computed_at < NOW() - INTERVAL '30 days';
 
--- Step 4: Add a partial index to speed up the NOT EXISTS check in the
+-- Step 6: Add a partial index to speed up the NOT EXISTS check in the
 -- aggregation propagation query
 CREATE INDEX IF NOT EXISTS idx_competitive_signals_source_doc_ticker
     ON competitive_signal_records (source_document_id, source_ticker);