Point the panel link at the installation, not at the browser's origin

Both links out of the dashboard editor were built root-relative, so a portal
serving the app under `/i/{id}` got a URL to itself: the hub has no route
there and answers a bare 404. That is what a device link and "open what a
wall panel sees" both landed on.

They want different answers. The view link is for the person already looking,
so it takes the router's basepath — `appPath` in `lib/portal` is the same
prefix the router applies to every `Link`, for the places that step outside
it. The device link is for a screen, which cannot go through the portal at
all: the shell is served only to a portal session, and the credential that
page carries is the portal's rather than the panel's. So the server now says
where it answers, and `FRONTEND_HOST` is that answer — the same setting the
password-reset links already use.

Also fixes the panel branch in the query error handler, which compared a raw
pathname and so never fired under a portal.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AHpLJHozysQXjsxAyU1WHj

frontend/src/components/Dashboard/DashboardEditor.tsx

@@ -51,6 +51,7 @@ import {
 import useCustomToast from "@/hooks/useCustomToast"
 import { useIsMobile } from "@/hooks/useMobile"
 import { slideUp, transitions } from "@/lib/motion"
+import { appPath } from "@/lib/portal"
 import { cn } from "@/lib/utils"
 import { handleError } from "@/utils"
 import {
@@ -644,7 +645,7 @@ export function DashboardEditor({
                 asChild
               >
                 <a
-                  href={`/view/${draft.name}`}
+                  href={appPath(`/view/${draft.name}`)}
                   target="_blank"
                   rel="noreferrer"
                 >

frontend/src/components/Dashboard/PanelsDialog.tsx

@@ -49,6 +49,11 @@ export function PanelsDialog() {
 
   const panels = config?.panels ?? []
   const known = dashboards?.data ?? []
+  // The installation's own address, not this browser's: administering through
+  // the portal puts the page on the portal's origin, and a screen cannot be
+  // sent there — it has no portal session and could not hold a panel
+  // credential if it had one.
+  const host = config?.frontend_host ?? ""
 
   const write = (next: PanelsConfig) =>
     save.mutate(next, {
@@ -67,7 +72,8 @@ export function PanelsDialog() {
         <DialogTitle>Panels</DialogTitle>
         <DialogDescription>
           A panel is one screen and the dashboards it shows. Point the device at
-          the link, and it asks for a code you enter here.
+          the link — the installation's own address, reachable from wherever the
+          screen hangs — and it asks for a code you enter here.
         </DialogDescription>
       </DialogHeader>
 
@@ -82,6 +88,7 @@ export function PanelsDialog() {
           <PanelRow
             key={panel.id}
             panel={panel}
+            host={host}
             dashboards={known.map((dashboard) => ({
               name: dashboard.name,
               title: dashboard.title || dashboard.name,
@@ -137,11 +144,14 @@ export function PanelsDialog() {
 
 function PanelRow({
   panel,
+  host,
   dashboards,
   onChange,
   onRemove,
 }: {
   panel: PanelDef
+  /** Where this installation answers, as it knows itself. */
+  host: string
   dashboards: { name: string; title: string }[]
   onChange: (next: PanelDef) => void
   onRemove: () => void
@@ -175,7 +185,7 @@ function PanelRow({
         : [...assigned, dashboard],
     })
 
-  const link = `${window.location.origin}/panel/${panel.id}`
+  const link = host ? `${host}/panel/${panel.id}` : ""
 
   return (
     <div className="grid gap-3" data-testid={`panel-${panel.id}`}>
@@ -240,6 +250,7 @@ function PanelRow({
         <Input
           readOnly
           value={link}
+          placeholder="This installation has no address set"
           aria-label={`Link for ${panel.id}`}
           className="text-muted-foreground"
           onFocus={(event) => event.currentTarget.select()}