refactor(web): unify offline/error fallback across pages

[gerardoparrajc]

Extracts the repeated if (!x.ok) return x.offline ? <Offline/> : <ErrorNotice/> check
into a shared resultFallback(result, prefix?) helper in components/offline.tsx, used
across the projects, project overview, settings, insights, agents, attention and stories
pages. Also routes a real 404 on project settings through notFound() instead of a
generic ErrorNotice.

Files affected:

• apps/web/components/offline.tsx

• apps/web/app/(app)/(org)/projects/page.tsx

• apps/web/app/(app)/projects/[projectId]/page.tsx

• apps/web/app/(app)/projects/[projectId]/settings/page.tsx

• apps/web/app/(app)/projects/[projectId]/insights/page.tsx

• apps/web/app/(app)/projects/[projectId]/agents/page.tsx

• apps/web/app/(app)/projects/[projectId]/attention/page.tsx

• apps/web/app/(app)/projects/[projectId]/stories/page.tsx

• apps/web/app/(app)/projects/[projectId]/stories/[number]/page.tsx

• Persistence/migration/compatibility: none.

• Security/permissions: none — presentation-only, no new data exposed.

• Cost/budget/observability/analytics/GitHub mirror: none.

• Known risks / follow-up: apps/(app)/layout.tsx, projects/[projectId]/layout.tsx, and
  (org)/settings/page.tsx were left untouched (different existing semantics, e.g. the
  settings page doesn't currently distinguish offline from a real error); tracked as
  follow-up, not fixed here to keep this change behavior-preserving.

• Release classification: non-breaking, not user-visible (pure refactor).

Verification:

• pnpm exec biome check <changed files> — clean
• pnpm --filter @facility/sdk build && pnpm --filter @facility/web build — pass