feat: unified gateway route table (static · proxy · remote)

The gateway does two things — reverse-proxy services and serve static
frontends — but the dashboard/API route table only ever showed the proxy
routes, so 'serving a frontend' and 'proxying a service' looked like unrelated
features and castle-app/power-graph-app were invisible in the route view.

Now there's one concept: a route maps an address (path '/foo' or host 'foo.lan')
to a target of one kind — static (a built dist served by file_server), proxy
(a local service port), or remote (a service on another node).

- core: caddyfile.py gains compute_routes() — the single source of truth for
  the route list; generate_caddyfile_from_registry renders it (output byte-for-
  byte identical, verified against the live Caddyfile). Adds a GatewayRoute
  dataclass.
- api: GatewayRoute model → {address, kind, target, name, node}; GET /gateway
  builds from compute_routes (incl. config for static frontends + mesh for
  remote), so the table matches what Caddy actually does.
- app: Gateway panel shows Address · Kind · Target for every route (static
  frontends + host routes now appear); program detail shows 'Reachable at
  /foo/ · served (static)' for static frontends.
- cli: 'castle gateway status' prints the full route table.
- docs: registry.md/design.md/CLAUDE.md describe routes as one concept with
  three target kinds.

core 94 / cli 24 / api 52 green; ruff + app build clean; Caddyfile unchanged.

app/src/pages/ProgramDetail.tsx

@@ -28,6 +28,16 @@ export function ProgramDetailPage() {
     )
   }
 
+  // A static frontend (frontend behavior, build outputs, no service) is served
+  // by the gateway in place — show where.
+  const buildOutputs = (deployment.manifest.build as { outputs?: string[] } | undefined)?.outputs
+  const servedAt =
+    deployment.behavior === "frontend" && deployment.services.length === 0 && buildOutputs?.length
+      ? deployment.id === "castle-app"
+        ? "/"
+        : `/${deployment.id}/`
+      : null
+
   return (
     <div className="max-w-3xl mx-auto px-6 py-8">
       <DetailHeader
@@ -101,6 +111,14 @@ export function ProgramDetailPage() {
               </span>
             </>
           )}
+          {servedAt && (
+            <>
+              <span className="text-[var(--muted)]">Reachable at</span>
+              <a href={servedAt} className="font-mono text-[var(--primary)] hover:underline">
+                {servedAt} <span className="text-[var(--muted)]">· served (static)</span>
+              </a>
+            </>
+          )}
         </div>
 
         {deployment.commands && Object.keys(deployment.commands).length > 0 && (