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.

castle-api/tests/test_health.py

@@ -252,20 +252,19 @@ class TestGateway:
         assert data["managed_count"] == 1
 
     def test_gateway_routes(self, client: TestClient) -> None:
-        """Returns proxy routes from deployed components."""
+        """Returns the full route table, tagged with kind + target."""
         response = client.get("/gateway")
         data = response.json()
-        routes = data["routes"]
-        assert len(routes) == 1
-        route = routes[0]
-        assert route["path"] == "/test-svc"
-        assert route["target_port"] == 19000
-        assert route["program"] == "test-svc"
+        route = next(r for r in data["routes"] if r["address"] == "/test-svc")
+        assert route["kind"] == "proxy"
+        assert route["target"] == "localhost:19000"
+        assert route["name"] == "test-svc"
         assert route["node"] == "test-node"
 
-    def test_gateway_routes_sorted(self, client: TestClient) -> None:
-        """Routes are sorted by path."""
+    def test_gateway_route_kinds_valid(self, client: TestClient) -> None:
+        """Every route declares a known kind."""
         response = client.get("/gateway")
         data = response.json()
-        paths = [r["path"] for r in data["routes"]]
-        assert paths == sorted(paths)
+        assert data["routes"]
+        for r in data["routes"]:
+            assert r["kind"] in ("static", "proxy", "remote")