Session-bind /api/route and /api/overpass

Today both proxies are effectively open to anyone who can set an
Origin header for trails.cool — a third party can use us as a free
BRouter/Overpass relay. Require a live planner session on every call
so abuse traffic costs the scraper a session row (observable,
revocable) before they can issue a single query.

Server:
- New `requireSession(id)` helper — returns the session row or a 401
  Response. Reused by both route handlers.
- `/api/route`: `sessionId` in body is now required and verified;
  rate-limit key always falls back to the session id.
- `/api/overpass`: new `X-Trails-Session` header, verified. Header
  keeps the session out of the request body so the body-keyed cache
  is unaffected.

Client plumbing:
- `useRouting(yjs, sessionId)` — sessionId goes into the /api/route
  body.
- `usePois(sessionId)` → `queryPois(..., sessionId)` → `X-Trails-Session`
  on the proxy call.
- `PlannerMap` + `YjsDebugPanel` gain a `sessionId` prop from
  `SessionView`.

Journal server-to-server:
- Demo-bot and `/api/v1/routes/compute` now POST `/api/sessions` to
  mint a throwaway planner session, then cite it on the forwarded
  `/api/route` call. Planner's `expire-sessions` cron cleans these up
  (7d window) so nothing needs explicit teardown.

Tests:
- 5 unit tests for `requireSession` covering missing / empty /
  non-string / unknown-session / valid-session cases.
- Two integration E2E tests document the 401 for missing session on
  each proxy.
- Pre-existing `/api/route` integration tests updated to mint a
  session first.

Caveat: existing browser tabs lose their /api/route ability until
reload (the old JS doesn't know to send sessionId). Acceptable for
an anonymous planner.

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

apps/planner/app/components/PlannerMap.tsx

@@ -88,6 +88,7 @@ function getWaypointsFromYjs(waypoints: Y.Array<Y.Map<unknown>>): WaypointData[]
 
 interface PlannerMapProps {
   yjs: YjsState;
+  sessionId: string;
   onRouteRequest?: (waypoints: WaypointData[]) => void;
   onImportError?: (message: string) => void;
   highlightPosition?: [number, number] | null;
@@ -362,10 +363,10 @@ function PoiRefresher({ poiState }: { poiState: ReturnType<typeof usePois> }) {
   return null;
 }
 
-export function PlannerMap({ yjs, onRouteRequest, highlightPosition, highlightedWaypoint, onRouteHover, onImportError, days }: PlannerMapProps) {
+export function PlannerMap({ yjs, sessionId, onRouteRequest, highlightPosition, highlightedWaypoint, onRouteHover, onImportError, days }: PlannerMapProps) {
   const { t } = useTranslation("planner");
   const [waypoints, setWaypoints] = useState<WaypointData[]>([]);
-  const poiState = usePois();
+  const poiState = usePois(sessionId);
   useProfileDefaults(yjs, poiState);
   useYjsPoiSync(yjs, poiState);
   const [enabledOverlays, setEnabledOverlays] = useState<string[]>([]);