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/lib/launcher-login-path.ts

@@ -0,0 +1,9 @@
+/** Normalize URL pathname for comparisons (trailing slashes, empty). */
+export function normalizePathname(p: string): string {
+  const t = p.replace(/\/+$/, "")
+  return t === "" ? "/" : t
+}
+
+export function isLauncherLoginPathname(pathname: string): boolean {
+  return normalizePathname(pathname) === "/launcher-login"
+}