feat(dashboard): always enable embedded chat; remove dashboard --tui flag

The dashboard's embedded Chat surface (/chat, /api/ws, /api/pty) was gated
behind `hermes dashboard --tui` / HERMES_DASHBOARD_TUI=1. The desktop app and
the dashboard's own Chat tab both drive the agent over the /api/ws + /api/pty
WebSockets, so a dashboard started without the flag would pass the /api/status
health check but slam the chat WebSocket shut with WS code 4403 — the app
connects, reports "ready", and chat stays dead. This was the root cause behind
multiple user reports of the desktop app failing to connect to a self-hosted
gateway/dashboard, and it bit Docker and host installs alike.

Make the embedded chat unconditional:

- web_server.py: _DASHBOARD_EMBEDDED_CHAT_ENABLED defaults to True; drop the
  embedded_chat parameter and the runtime reassignment from start_server().
  The WS gates still read the constant (now always true) so the seam — and its
  "rejects when disabled" contract test — stays meaningful.
- main.py: remove the `--tui` argument from the dashboard subparser and the
  `embedded_chat = args.tui or HERMES_DASHBOARD_TUI==1` derivation.
- web/: isDashboardEmbeddedChatEnabled() returns true unconditionally; drop the
  deprecated __HERMES_DASHBOARD_TUI__ alias and the dead LEGACY_TUI_RE scrape in
  the vite dev-token plugin.
- apps/desktop/electron/main.cjs: drop `--tui` from the spawned dashboardArgs
  (it would now error with "unrecognized arguments: --tui") and the redundant
  HERMES_DASHBOARD_TUI env injection.
- Docker: no s6 run-script change needed — the script never passed --tui; the
  HERMES_DASHBOARD_TUI env var is now simply a no-op, so the image works out of
  the box with no extra var.
- Docs: remove every dashboard --tui / HERMES_DASHBOARD_TUI reference across the
  CLI reference, env-var reference, docker/desktop/web-dashboard guides, in-app
  tips, and the zh-Hans translations. The terminal `hermes --tui` / HERMES_TUI
  references are intentionally left untouched.

Tests: 270 passing across web_server, dashboard lifecycle, host-header,
auth-gate, and docker-override-scripts suites.

web/vite.config.ts

@@ -19,8 +19,6 @@ function hermesDevToken(): Plugin {
   const TOKEN_RE = /window\.__HERMES_SESSION_TOKEN__\s*=\s*"([^"]+)"/;
   const EMBEDDED_RE =
     /window\.__HERMES_DASHBOARD_EMBEDDED_CHAT__\s*=\s*(true|false)/;
-  const LEGACY_TUI_RE =
-    /window\.__HERMES_DASHBOARD_TUI__\s*=\s*(true|false)/;
 
   return {
     name: "hermes:dev-session-token",
@@ -38,12 +36,7 @@ function hermesDevToken(): Plugin {
           return;
         }
         const embeddedMatch = html.match(EMBEDDED_RE);
-        const legacyMatch = html.match(LEGACY_TUI_RE);
-        const embeddedJs = embeddedMatch
-          ? embeddedMatch[1]
-          : legacyMatch
-            ? legacyMatch[1]
-            : "false";
+        const embeddedJs = embeddedMatch ? embeddedMatch[1] : "true";
         return [
           {
             tag: "script",