feat(web): protect launcher dashboard with token and SPA login (#1953)

Add token-based authentication for the Launcher's embedded Web Dashboard.

- Ephemeral token generated in-memory each run (or via PICOCLAW_LAUNCHER_TOKEN env var)
- HMAC-SHA256 session cookie (HttpOnly, SameSite=Lax, Secure when HTTPS)
- Bearer token support for API/script access
- Rate limiting on login (10 attempts/IP/min)
- Referrer-Policy: no-referrer on all responses
- POST-only logout with JSON content-type (CSRF-safe)
- System tray "Copy dashboard token" action
- Login page shows contextual help (console/tray/log file path)
- Path traversal protection via path.Clean
- X-Forwarded-Host/Port/Proto support for reverse proxy deployments
- Full i18n support (English, Chinese)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/frontend/src/api/system.ts

@@ -1,3 +1,5 @@
+import { launcherFetch } from "@/api/http"
+
 export interface AutoStartStatus {
   enabled: boolean
   supported: boolean
@@ -12,7 +14,7 @@ export interface LauncherConfig {
 }
 
 async function request<T>(path: string, options?: RequestInit): Promise<T> {
-  const res = await fetch(path, options)
+  const res = await launcherFetch(path, options)
   if (!res.ok) {
     let message = `API error: ${res.status} ${res.statusText}`
     try {