Split into a FastAPI backend and a React frontend, add case state and SSO

The single-file stdlib server became the limit: no way to track what had been
done about an alert, no accounts, and a UI that had to be hand-rolled in
template strings. This restructures it into something deployable.

Backend (FastAPI)
- app/ holds config, database, auth, delivery and the routers; triagelib keeps
  the triage engine unchanged, so the validated screening and runbook logic is
  untouched.
- Cases persist per alert fingerprint with a status workflow (investigating,
  customer contacted, escalated to Infra, waiting, remediated, resolved, won't
  fix, false positive), an assignee, notes and an append-only history. An alert
  that stops and re-fires lands back on the same case and counts as a reopen.
- Suppression rules move from a JSON file into the database.

Auth
- Signed session cookies over PBKDF2 local accounts, plus an OIDC flow ready for
  Authentik: users are created on first login and admin follows a group claim.
  Local login can be switched off entirely once SSO is live.

Zendesk and Jira
- Delivery is now implemented, behind three gates: the integration must be
  configured, its feature flag on, and CX_FEATURE_SEND_ENABLED on. A demo
  instance leaves the last off and cannot mail anyone. Both search before
  creating, so re-diagnosing an alert updates one ticket rather than opening
  several, and a rolling daily cap stops a loop mailing everybody.

Deployment
- Multi-stage Dockerfile builds the bundle and serves it from the API origin.
- docker-compose for local and single-host use; Gitea Actions runs the tests,
  builds the image and renders deploy/k8s with envsubst.

Two fixes found while testing: assigning a case returned a null assignee, and
add_event could leave an already-loaded history collection stale.

Known gap: the engine reaches OpenStack via `docker exec <region>-osc`, which
does not work in a pod without the CX-Tools containers alongside it.
docs/DEPLOYMENT.md sets out the three ways to close that.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

deploy/k8s/10-config.yaml

@@ -0,0 +1,30 @@
+# Non-secret configuration. Secrets live in the `cx-triage` Secret, created by
+# the pipeline from the repository secret store.
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: cx-triage-config
+  namespace: ${NAMESPACE}
+data:
+  CX_APP_NAME: "CX Triage"
+  CX_BASE_URL: "${BASE_URL}"
+  CX_SESSION_HOURS: "12"
+  CX_STATIC_DIR: "/app/static"
+
+  CX_PROMETHEUS_BASE: "${PROMETHEUS_BASE}"
+
+  CX_AUTH_LOCAL_ENABLED: "false"
+  CX_OIDC_ENABLED: "${OIDC_ENABLED}"
+  CX_OIDC_ISSUER: "${OIDC_ISSUER}"
+  CX_OIDC_SCOPES: "openid email profile"
+  CX_OIDC_ADMIN_GROUP: "${OIDC_ADMIN_GROUP}"
+  CX_OIDC_GROUPS_CLAIM: "groups"
+
+  CX_FEATURE_SEND_ENABLED: "${FEATURE_SEND_ENABLED}"
+  CX_FEATURE_ZENDESK: "${FEATURE_ZENDESK}"
+  CX_FEATURE_JIRA: "${FEATURE_JIRA}"
+  CX_FEATURE_LINKAGE_SCAN: "${FEATURE_LINKAGE_SCAN}"
+  CX_SEND_DAILY_CAP: "${SEND_DAILY_CAP}"
+
+  CX_JIRA_PROJECT: "${JIRA_PROJECT}"
+  CX_JIRA_ISSUE_TYPE: "Task"