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>

backend/app/routers/cases_router.py

@@ -0,0 +1,99 @@
+"""Case state: the human layer over the alert queue."""
+from __future__ import annotations
+
+import datetime as dt
+
+from fastapi import APIRouter, Depends, HTTPException, status
+from pydantic import BaseModel
+from sqlalchemy.orm import Session
+
+from ..auth import current_user
+from ..db import get_db
+from ..models import Case, CaseStatus, User
+from ..services import add_event, set_status
+
+router = APIRouter(prefix="/api/cases", tags=["cases"])
+
+
+class StatusBody(BaseModel):
+    status: str
+    note: str = ""
+
+
+class NoteBody(BaseModel):
+    note: str
+
+
+class SnoozeBody(BaseModel):
+    hours: int = 24
+    note: str = ""
+
+
+def _case(db: Session, fingerprint: str) -> Case:
+    found = db.query(Case).filter(Case.fingerprint == fingerprint).one_or_none()
+    if not found:
+        raise HTTPException(status.HTTP_404_NOT_FOUND, "No case for that alert yet")
+    return found
+
+
+@router.get("")
+def list_cases(open_only: bool = True, limit: int = 200, db: Session = Depends(get_db),
+               user: User = Depends(current_user)):
+    query = db.query(Case).order_by(Case.last_seen_at.desc())
+    rows = [c for c in query.limit(max(1, min(limit, 1000))).all()
+            if (c.is_open or not open_only)]
+    return {"cases": [c.to_json() for c in rows], "statuses": [s.value for s in CaseStatus]}
+
+
+@router.get("/{fingerprint}")
+def get_case(fingerprint: str, db: Session = Depends(get_db), user: User = Depends(current_user)):
+    return _case(db, fingerprint).to_json(with_events=True)
+
+
+@router.post("/{fingerprint}/status")
+def change_status(fingerprint: str, body: StatusBody, db: Session = Depends(get_db),
+                  user: User = Depends(current_user)):
+    try:
+        new_status = CaseStatus(body.status)
+    except ValueError as exc:
+        raise HTTPException(status.HTTP_400_BAD_REQUEST,
+                            f"Unknown status '{body.status}'") from exc
+    case = set_status(db, _case(db, fingerprint), new_status, user, body.note)
+    return case.to_json(with_events=True)
+
+
+@router.post("/{fingerprint}/assign")
+def assign(fingerprint: str, db: Session = Depends(get_db), user: User = Depends(current_user)):
+    case = _case(db, fingerprint)
+    # Set the relationship, not just the id: the response is serialised from
+    # this same object and a bare id leaves `assignee` null in the payload.
+    case.assignee = user
+    if case.status == CaseStatus.NEW:
+        case.status = CaseStatus.INVESTIGATING
+    add_event(db, case, user, "assigned", f"Picked up by {user.email}")
+    db.commit()
+    db.refresh(case)
+    return case.to_json(with_events=True)
+
+
+@router.post("/{fingerprint}/note")
+def add_note(fingerprint: str, body: NoteBody, db: Session = Depends(get_db),
+             user: User = Depends(current_user)):
+    if not body.note.strip():
+        raise HTTPException(status.HTTP_400_BAD_REQUEST, "Empty note")
+    case = _case(db, fingerprint)
+    case.notes = (case.notes + "\n" if case.notes else "") + body.note.strip()
+    add_event(db, case, user, "note", body.note.strip())
+    db.commit()
+    return case.to_json(with_events=True)
+
+
+@router.post("/{fingerprint}/snooze")
+def snooze(fingerprint: str, body: SnoozeBody, db: Session = Depends(get_db),
+           user: User = Depends(current_user)):
+    case = _case(db, fingerprint)
+    until = dt.datetime.now(dt.timezone.utc) + dt.timedelta(hours=max(1, body.hours))
+    case.snooze_until = until
+    add_event(db, case, user, "snoozed", f"Snoozed for {body.hours}h. {body.note}".strip())
+    db.commit()
+    return case.to_json(with_events=True)