device: add copyToClipboard and fix regenerate token HTMX button

Phase 3: Complete device page functionality fixes

- Add copyToClipboard function to device-management.ts:
  - Uses navigator.clipboard.writeText() for copying
  - Shows success/error toast notifications
  - Already exported in Alpine.store, now properly defined
- Fix typo in devices.templ: change 'regerate-token' to 'regenerate-token'
- Add HTMX support to RegenerateDeviceToken handler:
  - Returns HTML with reload script for HTMX requests
  - Preserves JSON response for API calls

The regenerate token button now works via HTMX (hx-put) instead of
Alpine.js, matching the pattern used elsewhere in the app.

internal/handlers/devices.go

@@ -554,6 +554,11 @@ func (h *DeviceHandler) RegenerateDeviceToken(c *echo.Context) error {
 		syncURLs["bookmarks"] = fmt.Sprintf("%s/api/sync/koreader/bookmarks", baseURL)
 	}
 
+	// Handle HTMX requests - return HTML with page reload script
+	if c.Request().Header.Get("HX-Request") == "true" {
+		html := fmt.Sprintf(`<div class="text-green-500">Token regenerated! Reloading ... </div><script>window.location.reload();`)
+		return c.HTML(http.StatusOK, html)
+	}
 	return c.JSON(http.StatusOK, map[string]interface{}{
 		"message":    "Token regenerated successfully",
 		"auth_token": newToken,