feat: dashboard OAuth provider management

Add OAuth provider management to the Hermes dashboard with full
lifecycle support for Anthropic (PKCE), Nous and OpenAI Codex
(device-code) flows.

## Backend (hermes_cli/web_server.py)

- 6 new API endpoints:
  GET /api/providers/oauth — list providers with connection status
  POST /api/providers/oauth/{id}/start — initiate PKCE or device-code
  POST /api/providers/oauth/{id}/submit — exchange PKCE auth code
  GET /api/providers/oauth/{id}/poll/{session} — poll device-code
  DELETE /api/providers/oauth/{id} — disconnect provider
  DELETE /api/providers/oauth/sessions/{id} — cancel pending session
- OAuth constants imported from anthropic_adapter (no duplication)
- Blocking I/O wrapped in run_in_executor for async safety
- In-memory session store with 15-minute TTL and automatic GC
- Auth token required on all mutating endpoints

## Frontend

- OAuthLoginModal — PKCE (paste auth code) and device-code (poll) flows
- OAuthProvidersCard — status, token preview, connect/disconnect actions
- Toast fix: createPortal to document.body for correct z-index
- App.tsx: skip animation key bump on initial mount (prevent double-mount)
- Integrated into the Env/Keys page

web/src/main.tsx

@@ -1,10 +1,7 @@
-import { StrictMode } from "react";
 import { createRoot } from "react-dom/client";
 import "./index.css";
 import App from "./App";
 
 createRoot(document.getElementById("root")!).render(
-  <StrictMode>
-    <App />
-  </StrictMode>,
+    <App />,
 );