monitoring: consolidate all Slack alerting to #alerts, abandon #security

The dedicated #security Slack channel was unreachable: the shared incoming
webhook (Vault secret/viktor -> alertmanager_slack_api_url) belongs to a
Slack app that isn't a member of #security, so any channel override on it
returns HTTP 404 channel_not_found. The goldmane-edges-digest was silently
failing for that reason.

Per request ("dump the security channel, post in an existing one"), route
everything to #alerts instead:
- alertmanager slack-security receiver -> #alerts (keeps its [SECURITY/<sev>]
  title styling so security-lane alerts still stand out in the shared channel)
- goldmane-edges-digest CronJob SLACK_CHANNEL -> #alerts (comment only; value
  was already switched and applied last change)
- AggregatorDown / DigestFailing alert summaries reworded to say #alerts
- docs swept (security.md, monitoring.md, ADR-0014, goldmane runbook,
  .claude/CLAUDE.md, service-catalog, CONTEXT.md) to drop the
  "invite the app / flip back to #security" caveats and state the
  #security abandonment + #alerts consolidation as the current routing.

Monitoring stack applied (alertmanager rolled, live config verified:
slack-security channel is now #alerts).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/adr/0014-service-identity-and-east-west-observability.md

@@ -30,6 +30,6 @@ As the Service count grows we want an audit-grade record of which Service talks
 
 ## As-built (2026-06-25)
 
-Implemented across infra issues #57–#63. **One material deviation from the decision above:** the durable trail is NOT a Goldmane→Loki emitter (no such emitter exists in OSS Calico 3.30) — it is the **`goldmane-edge-aggregator`** service, which streams Goldmane's gRPC `Flows.Stream` API over mTLS and upserts the unique namespace-pair **edge set** (`edge(src_ns,dst_ns,action,first_seen,last_seen,flow_count)`, self-edges + empty-namespace flows dropped) into **CNPG DB `goldmane_edges`**, plus a daily `goldmane-edges-digest` CronJob → `#alerts` (the shared webhook can't reach `#security` — see runbook). The mTLS client cert **reuses the operator's Tigera-CA-signed `whisker-backend-key-pair`** rather than copying the CA private key into TF state (Goldmane verifies CA-chain only, not identity) — re-apply `stacks/goldmane-edge-aggregator` if the operator rotates it. `service-identity` labels are live on the multi-Service namespaces (`monitoring`, `dbaas`). Whisker UI is Authentik-gated at `whisker.viktorbarzin.me`. Health: Prometheus alerts `AggregatorDown` + `DigestFailing` and cluster-health check #48.
+Implemented across infra issues #57–#63. **One material deviation from the decision above:** the durable trail is NOT a Goldmane→Loki emitter (no such emitter exists in OSS Calico 3.30) — it is the **`goldmane-edge-aggregator`** service, which streams Goldmane's gRPC `Flows.Stream` API over mTLS and upserts the unique namespace-pair **edge set** (`edge(src_ns,dst_ns,action,first_seen,last_seen,flow_count)`, self-edges + empty-namespace flows dropped) into **CNPG DB `goldmane_edges`**, plus a daily `goldmane-edges-digest` CronJob → `#alerts` (all Slack consolidated to `#alerts`; the `#security` channel was abandoned 2026-06-25 — the shared webhook's Slack app isn't a member of it — see runbook). The mTLS client cert **reuses the operator's Tigera-CA-signed `whisker-backend-key-pair`** rather than copying the CA private key into TF state (Goldmane verifies CA-chain only, not identity) — re-apply `stacks/goldmane-edge-aggregator` if the operator rotates it. `service-identity` labels are live on the multi-Service namespaces (`monitoring`, `dbaas`). Whisker UI is Authentik-gated at `whisker.viktorbarzin.me`. Health: Prometheus alerts `AggregatorDown` + `DigestFailing` and cluster-health check #48.
 
 Full as-built, query recipes (incl. the Wave-1 egress-allowlist derivation), and troubleshooting: [`docs/runbooks/goldmane-flow-trail.md`](../runbooks/goldmane-flow-trail.md). Stacks: `stacks/calico` (Goldmane/Whisker + Whisker ingress), `stacks/goldmane-edge-aggregator` (the trail). Code: `~/code/goldmane-edge-aggregator`.