fix: distinguish filtered object empty states

[cxymds]

Summary

• distinguish a genuinely empty bucket from an empty client-side filter result
• show separate states while additional object batches are loading or remain unsearched
• add localized copy across all Console locales
• add unit and source-level regression coverage for the object-list state contract

Root cause

The object browser filtered only the objects already loaded in the client, but always reused the genuine empty-bucket copy when that filtered set was empty. This could incorrectly tell operators that a populated bucket had no objects.

User impact

Filtered searches no longer display the empty-bucket upload prompt. The UI now explains whether more objects remain unsearched or whether all loaded objects have been checked.

Closes #183

Validation

• pnpm install --frozen-lockfile
• pnpm test:run (367/367 passed)
• pnpm tsc --noEmit
• pnpm lint
• git diff origin/main --check
• changed files pass Prettier

Repository-wide pnpm prettier --check . still reports the existing formatting issue in app/(dashboard)/sse/page.tsx; that file is unchanged by this PR.