feat: add scrape job result persistence for effectiveness tracking

migrations/20260131100000_add_scrape_job_results.sql

@@ -0,0 +1,31 @@
+-- Scrape job results log: one row per completed (or failed) job for effectiveness tracking.
+CREATE TABLE scrape_job_results (
+    id              BIGSERIAL PRIMARY KEY,
+    target_type     target_type NOT NULL,
+    payload         JSONB NOT NULL,
+    priority        scrape_priority NOT NULL,
+
+    -- Timing
+    queued_at       TIMESTAMPTZ NOT NULL,
+    started_at      TIMESTAMPTZ NOT NULL,
+    completed_at    TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    duration_ms     INT NOT NULL,
+
+    -- Outcome
+    success         BOOLEAN NOT NULL,
+    error_message   TEXT,
+    retry_count     INT NOT NULL DEFAULT 0,
+
+    -- Effectiveness (NULL when success = false)
+    courses_fetched     INT,
+    courses_changed     INT,
+    courses_unchanged   INT,
+    audits_generated    INT,
+    metrics_generated   INT
+);
+
+CREATE INDEX idx_scrape_job_results_target_time
+    ON scrape_job_results (target_type, completed_at);
+
+CREATE INDEX idx_scrape_job_results_completed
+    ON scrape_job_results (completed_at);