fix and adjust main dashboard ai insight

backend/database/erd_schema.sql

@@ -196,7 +196,6 @@ CREATE TABLE IF NOT EXISTS ai_insight (
     topic         VARCHAR(64)  NOT NULL DEFAULT '',
     report_type   VARCHAR(32)  NOT NULL DEFAULT 'page',
     report_period VARCHAR(64)  NOT NULL DEFAULT 'current',
-    source        VARCHAR(32)  NOT NULL DEFAULT 'generated',  -- generated | cache | local_fallback
     summary       TEXT         NOT NULL DEFAULT '',
     citations     TEXT         NOT NULL DEFAULT '[]',  -- JSON array string of RAG citations
     created_at    TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT CURRENT_TIMESTAMP,