docs: reconcile scheduler topology across sibling docs (7 → 12 loops)

Authoritative 12-loop table lives at docs/architecture.md:522-534 (committed via
the I-001/I-003/I-005 + M48/M50 milestone commits). This change brings six sibling
docs into parity with that table so every surface — user-facing features reference,
SOC 2 compliance mapping, connectors guide, advanced demo architecture diagram,
testing guide, and in-line architecture prose — reflects the same 8 always-on + 4
opt-in topology.

Touches:
- docs/architecture.md: 2 inline ordinal references (9th / 8th loop) replaced with
  descriptive names (opt-in cloud discovery / opt-in endpoint health), cross-linked
  to the authoritative table to prevent future ordinal rot.
- docs/features.md: metric row (7 → 12), inline reference to 9th loop, and full
  scheduler table expanded to include Always-on column + env vars + I-001/I-003/I-005
  refs.
- docs/compliance-soc2.md: background scheduler monitoring bullets expanded to list
  all 12 loops with env vars + I-series refs; table row updated with 8 always-on +
  4 opt-in summary.
- docs/connectors.md: three inline ordinals (7th/6th/9th loop) replaced with
  descriptive names, cross-linked to architecture.md.
- docs/demo-advanced.md: Mermaid SCHED node label updated from '7 background loops'
  to '12 background loops (8 always-on + 4 opt-in)'.
- docs/testing-guide.md: Test 20.1.1 header + grep pattern expanded to include
  job-retry / job-timeout / notification-retry / digest / endpoint-health /
  cloud-discovery loops; sign-off chart row label updated.

Pure documentation reconciliation. No code changes. Master HEAD pre-commit: 6e646e0.

docs/demo-advanced.md

@@ -1155,7 +1155,7 @@ flowchart TB
         API["REST API\nGo net/http"]
         SVC["Service Layer\nBusiness Logic"]
         REPO["Repository Layer\ndatabase/sql + lib/pq"]
-        SCHED["Scheduler\n7 background loops"]
+        SCHED["Scheduler\n12 background loops\n(8 always-on + 4 opt-in)"]
         CONN["Connector Registry\nIssuer + Target + Notifier"]
     end