fix: keep large cleanup result groups responsive

[n9896027]

Result

• Paginate large cleanup candidate groups at 40 rows per page.
• Keep groups above 24 items collapsed by default.
• Add Previous/Next controls and English, Simplified Chinese, and Traditional Chinese copy.
• Add regression coverage for first, middle, final, empty, and out-of-range pages.

Reproduction and evidence

Before the fix, expanding a 408-item audio group raised the app to about 2.1 GB RSS immediately; the accumulated failure reached about 9.7 GB RSS and nearly 100% CPU, leaving the SwiftUI window unresponsive.

With the fix, the same 512-candidate scan (including the 408-item audio group) remained responsive while paging, at about 0.47–0.51 GB during the loaded scan. After a clean relaunch on Overview, the app settled around 100 MB in the sampled process view.

No cleanup, move, or deletion operation was executed during verification.

Risk boundaries

• UI presentation and a pure pagination window model only.
• Does not change scan roots, candidate eligibility, selection policy, trash behavior, permissions, process control, networking, or AI authority.
• Existing deletion and recovery safeguards remain unchanged.

Local verification

• git diff --check
• Current-tree repository audit: no potential credential signals found in the scanned scope
• Staged privacy/credential pattern scan: no matches
• swift test: 184 tests, 1 skipped, 0 failures
• swift run CleanNestSelfTest: passed
• ./build.sh release: passed
• App, MCP, login item, and scanner signature verification: passed
• Real UI pagination through the large audio group: responsive

Remote verification

• CI
• Dependency review
• CodeQL

Release state

This is a Draft PR for the next hotfix candidate. It does not merge, tag, or publish a Release. The generated local bundle uses the existing stable local signing identity; it is not Developer ID signed or Apple notarized.