Migrate inline ff-dialog usages to the universal modal system

[cstns]

Migrate the ~9 inline ff-dialog usages scattered across pages and components to the universal modal system. These are raw ff-dialog elements defined directly in page templates, toggled by data properties.

Known locations:

• pages/application/DeviceGroups.vue
• pages/application/PipelineStage/form.vue
• pages/admin/Settings/General.vue
• pages/admin/Template/sections/Environment.vue
• pages/device/Settings/General.vue
• pages/team/DeviceGroups/index.vue
• components/DevicesBrowser.vue
• components/expert/components/ExpertChatInput.vue
• components/file-browser/FileBrowser.vue

Part of #8144, #8122.