Fix bucket assignment

The home page ran its own /api/auth/session check to decide whether to
render, while the bucket list is driven by BucketContext -> AuthContext.user
(a separate check). When the two resolved out of sync the page rendered with
an empty bucket list, and BucketContext had no loading state so an
unpopulated list was indistinguishable from a genuinely empty one and never
retried.

- page.tsx: consume useAuth() instead of a bespoke session fetch, so page
  gating and data loading share one session resolution (removes a redundant
  network call).
- BucketContext: add isLoading (true until the authenticated user's buckets
  have been fetched); home page shows a spinner until then instead of
  flashing an empty list.
- e2e: drop the reload() workaround that masked the bug.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

E2E tests for bucket management + AuthContext session race fix

Writing uploads to public/ breaks under output: 'standalone' — the dir is
a build-time snapshot, so runtime-written files 404 (broken image on EC2).
Store logo bytes in app_settings and stream them from a dynamic route.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Corporate avanse theme

Upload controls: malware scanning with clean/unscanned indicators