fix(dashboard): respect HERMES_BASE_PATH in WebSocket URLs (#25547)

When the dashboard is reverse-proxied under a path prefix
(`X-Forwarded-Prefix: /dashboard`), the SPA already routes its
`/api/...` REST traffic through `HERMES_BASE_PATH` via
`web/src/lib/api.ts`. Three WebSocket URLs constructed elsewhere
were still hardcoded to root `/api/...` and so opened
`wss://host/api/...` instead of `wss://host/dashboard/api/...`,
forcing operators to forward selected root API/WS paths through the
reverse proxy as a workaround (see issue #25547).

Add `HERMES_BASE_PATH` between `host` and `/api/...` in the
three constructed WebSocket URLs:

- `web/src/pages/ChatPage.tsx` — PTY WebSocket
- `web/src/components/ChatSidebar.tsx` — events subscriber
- `web/src/lib/gatewayClient.ts` — JSON-RPC gateway WebSocket

When the dashboard is served at root, `HERMES_BASE_PATH === """
and the URLs are bit-for-bit identical to before. Under a prefix,
the WebSocket connections now go through the same proxy path the
REST calls already use.

Note: bundled dashboard plugins (kanban, hermes-achievements) embed
`"/api/plugins/..."` in their compiled `dist/index.js` and
remain out of scope here — those need source-side fixes per plugin.

Fixes #25547.

web/src/pages/ChatPage.tsx

@@ -24,6 +24,7 @@ import { Terminal } from "@xterm/xterm";
 import "@xterm/xterm/css/xterm.css";
 import { Button } from "@nous-research/ui/ui/components/button";
 import { Typography } from "@/components/NouiTypography";
+import { HERMES_BASE_PATH } from "@/lib/api";
 import { cn } from "@/lib/utils";
 import { Copy, PanelRight, X } from "lucide-react";
 import { useCallback, useEffect, useMemo, useRef, useState } from "react";
@@ -44,7 +45,7 @@ function buildWsUrl(
   const proto = window.location.protocol === "https:" ? "wss:" : "ws:";
   const qs = new URLSearchParams({ token, channel });
   if (resume) qs.set("resume", resume);
-  return `${proto}//${window.location.host}/api/pty?${qs.toString()}`;
+  return `${proto}//${window.location.host}${HERMES_BASE_PATH}/api/pty?${qs.toString()}`;
 }
 
 // Channel id ties this chat tab's PTY child (publisher) to its sidebar