feat(insights): permanent archive of PostHog events + raw recordings

Phase A of the external observability archive. PostHog Cloud free tier
deletes data on a rolling window (events ~1yr, session recordings ~30d);
this mirrors both into our own infra permanently (hot Postgres + cold
MinIO gzip JSONL).

PostHog raw event archive:
- New `PosthogEvent` model (uuid PK → dedup, full properties JSONB,
  hot columns promoted + indexed).
- `posthog-event-archive` job: watermark-paged HogQL pull (cursor in the
  existing IngestionWatermark via a "sase:events" stream key), createMany
  + skipDuplicates for idempotency, 365d backfill. Daily closed-day cold
  dump to MinIO `posthog-archive/{project}/YYYY/MM/DD.jsonl.gz`.
- `hogqlQuery` helper added to posthog.ts. Timestamp cursor uses
  parseDateTimeBestEffort() — ClickHouse 500s on a raw ISO8601 literal
  (verified live against the project).

Raw rrweb recording preservation (separate from compress, which only
covers scored sessions and caps blobs):
- `SessionMeta.rrwebArchivedAt` / `rrwebArchiveKey`.
- `archive-recordings` job: every recording within 25d (margin before
  30d deletion), full blob range (no 12-cap), gzip → MinIO
  `rrweb-archive/{project}/YYYY/MM/DD/{sessionId}.jsonl.gz`.

- `putBuffer` gzip helper in minio.ts.
- Both jobs wired into pipeline.ts (event-archive@*/15min, recordings@*/6h).
- retention.ts untouched → new table + buckets persist forever (the goal).

Schema applies via the existing `prisma db push` on web start (additive:
new table + nullable columns).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/prisma/schema.prisma

@@ -142,6 +142,10 @@ model SessionMeta {
   processedAt       DateTime?
   createdAt         DateTime @default(now())
 
+  // Raw rrweb recording preservation (archived to MinIO before PostHog's ~30-day deletion).
+  rrwebArchivedAt   DateTime?
+  rrwebArchiveKey   String?
+
   compressed        CompressedSession?
 
   @@index([status, createdAt])
@@ -445,3 +449,27 @@ model SaseUserNote {
   @@index([saseUserId, pinned, createdAt])
   @@map("sase_user_notes")
 }
+
+// ---------- Phase 9: External Observability Archive ----------
+
+// PostHog raw event stream mirrored to our DB permanently (free tier deletes
+// events on a rolling window). Lossless: full properties kept as JSONB, with
+// hot fields promoted to indexed columns. Also cold-dumped to MinIO as gzip JSONL.
+model PosthogEvent {
+  uuid        String   @id            // PostHog event uuid → natural dedup key
+  projectKey  String                  // "sase"
+  event       String
+  distinctId  String
+  personId    String?
+  sessionId   String?                 // $session_id — joins to SessionMeta.id
+  timestamp   DateTime                // PostHog event time
+  properties  Json                    // full properties — lossless
+  ingestedAt  DateTime @default(now())
+  dumpedAt    DateTime?               // set once written to MinIO cold partition
+
+  @@index([projectKey, timestamp])
+  @@index([event, timestamp])
+  @@index([distinctId, timestamp])
+  @@index([dumpedAt])
+  @@map("posthog_events")
+}