Harden complete container loading

[mkaltner]

Summary

• retain Arcane's documented limit = -1 show-all container request introduced in Fix Containers tab completeness and activity stream events #39
• harden complete-list integrity with container-ID deduplication and reported-total validation so partial or inconsistent results are not published
• propagate coroutine cancellation and extract deterministic filtering/loading-state logic for focused regression coverage
• record PAR-003 validation evidence and a scoped PAR-004 follow-up for the broader pagination audit

Context

PR #39 already fixed the user-visible first-20 issue by switching the Containers screen to Arcane's documented show-all contract. This PR does not introduce bounded page traversal: the available server sorts do not provide a unique ordering key needed for correctness-preserving offset traversal.

Instead, this follow-up verifies and hardens the existing complete-list behavior. Local search and filters operate only after the intended dataset is confirmed complete, duplicate IDs cannot produce duplicate UI results, inconsistent totals fail without publishing partial content, and cancellation remains structured.

No Kotlin SDK, Arcane server, or Arcane Updates changes are included.

Validation

• focused pagination tests: 14/14 passed
• :app:testDebugUnitTest: 98/98 passed
• :app:assembleDebug: passed
• git diff --check: passed (Windows line-ending warnings only)

Manual device testing is pending.