fix: use grouped apps endpoint on initial load, fall back to per-namespace polling

[dcharles525]

PR Checklist

• Linting Test is passing
• Code is well documented
• If applicable, a PR in the epinio/docs repository has been opened

Summary

Fixes the initial app list page performance issue where one API call was fired per namespace on load.

Pairs with epinio/epinio#3034.

Occurred changes and/or fixed issues

• Added findGroupedApps store action that calls the new /api/v1/applications/grouped endpoint
• onMounted now uses findGroupedApps for the initial load (1 call, server-side fan-out) instead of per-namespace calls
• Per-namespace pagination and background polling continue using the existing findAppsInNamespace action unchanged
• Increased polling interval to reduce steady-state load on the server

Technical notes summary

The grouped endpoint returns map[namespace]PaginatedResponse. The store action guards against epiniofy injecting non-namespace keys into the response map before classifying items.

Areas or cases that should be tested

• App list page loads correctly across multiple namespaces
• Per-namespace table pagination still works after initial load
• Background polling still refreshes app state
• A user with no namespace access sees an empty list, not an error

Areas which could experience regressions

• App list page initial render
• Per-namespace table pagination state

[johnlcos]

LGTM

[johnlcos]

LGTM