Applications 4 - remaining vue + loaders

[n-lark]

PR — remaining vue + loaders

• pages/application/index.vue + mixins/Application.js read the store (activeApplication; context.application becomes a pass-through like context.team) instead of local fetch; add activeApplicationId/activeApplication/setActiveApplication.

• Page Loader for the application detail; Component Loaders for sub-widgets (e.g. the instance table) so the shell stays interactive.

• Delete dead fetching in mixins/Application.js.

• Instances still load via the existing path until the Hosted Instances store lands; add the joined getter then.

• Single-application views consume the store.

• Page/Component Loaders during load.

Test plan

• Cold load team → applications list from store behind a Page Loader.
• Create application via expert/MCP while on the list → appears without reload.
• Create via the form → appears / navigates, no stale list.
• Delete application → removed from list without reload.
• After backend+subscriber: create/delete in another tab → reflected here.
• Navigate app→app → no refetch of the already-loaded team list.
• Switch team → list clears and reloads for the new team.