feat(db): discovery_snapshots table — daily Discovery-Tracking storage (P2 sub-step)

migrations/2026-05-21_create_discovery_snapshots.sql

@@ -0,0 +1,30 @@
+-- Discovery-Tracking-Baseline P2 (SPEC docs/specs/2026-05-21_discovery-tracking-baseline-SPEC.md §3.5 + §4)
+--
+-- Daily snapshot table for Discovery surfaces:
+--   - GSC indexed URLs / impressions / clicks / crawl frequency
+--   - nginx bot-hits per User-Agent × endpoint-class
+--   - GitHub Stars/Forks/Clones/Views for MoltyCel/* repos
+--   - Self-Probe pass/fail (sitemap.xml, llms.txt, /guard/openapi.json, /extendedAgentCard)
+--
+-- Schema: BIGSERIAL pk + DATE-unique + JSONB payload (schema-flexible for V1
+-- iteration without ALTER TABLE migrations).
+--
+-- Run via P3 cron 00:30 UTC daily (scripts/discovery_snapshot.py — separate PR).
+-- Baseline row for 2026-05-21 inserted manually after this migration applies.
+
+CREATE TABLE IF NOT EXISTS discovery_snapshots (
+  id           BIGSERIAL PRIMARY KEY,
+  snapshot_at  DATE        NOT NULL UNIQUE,
+  generated_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+  payload      JSONB       NOT NULL,
+  source_run_status TEXT   NOT NULL DEFAULT 'ok'
+    CHECK (source_run_status IN ('ok','partial','failed'))
+);
+
+CREATE INDEX IF NOT EXISTS idx_discovery_snapshots_at
+  ON discovery_snapshots(snapshot_at DESC);
+
+COMMENT ON TABLE discovery_snapshots IS
+  'Daily Discovery-Tracking snapshots. One row per day. payload-JSONB shape per SPEC §3.5.';
+COMMENT ON COLUMN discovery_snapshots.source_run_status IS
+  'ok = all 5 sources captured · partial = some sources failed (see payload.errors) · failed = none captured';