General: Smoother multi-select on tool lists

[d4rken]

What changed

When you select multiple items in a tool's list or detail screen (apps, files, duplicates, exclusions…), tapping each item used to make the whole visible list redo work for every row — re-loading thumbnails and re-formatting sizes/dates/counts on every tap. On lower-end devices that showed up as lag while multi-selecting. Now tapping an item only updates that one row, so multi-select stays smooth even on long lists. Nothing about how selection looks or behaves changes.

Technical Context

• Root cause: every list/detail screen read the selection Set (selection.contains(id) / selection.isNotEmpty()) inside its items{} lambda, so every visible row subscribed to the single MutableState<Set<T>> and recomposed on every toggle — re-running its leaf work (thumbnails, formatShortFileSize, plurals, date formatters).
• Fix: new @Stable SelectionState<T> holder (app-common-ui/.../compose/selection/) exposing per-id membership via @Composable isSelected(id) backed by derivedStateOf, so only the row whose membership flips recomposes. isActive/count are derivedStateOf too, so the container/top bar recompose only on the selection-mode transition / count change, not on every toggle. Replaces and deletes the old rememberSelection helper.
• Scope: all 13 call sites migrated. Screen-scope aggregate reads that would have re-invalidated the list (Squeezer "savings", Analyzer "selected items / none inaccessible") were moved into the top-bar composables. Container composables CorpseContent / AppJunkPage / FilterContentPage / ClusterContent now take the holder. AppControl's pendingExportIds was migrated too so the old helper had no remaining callers.
• Deduplicator (data safety): the details screen's keep-one delete cap is preserved on toggle/long-press/select-all, and is now also re-applied after the live-id prune — closing a pre-existing gap where a cluster shrinking under a held selection (or a saved selection restored against a smaller cluster) could let a delete take the entire cluster. Verified on-device: a 3-item cluster caps selection at 2.
• Out of scope: the Deduplicator list selectedDupes delete-target model (a separate VM-owned mechanism, not rememberSelection).

Review guidance

• The isolation contract lives in SelectionState.isSelected — SelectionStateIsolationTest proves a steady-active toggle recomposes only the toggled row, and documents the expected all-row recompose on the empty↔non-empty transition.
• The non-mechanical migration is DeduplicatorDetailsScreen + ClusterContent (cluster clip via selectionEnabled && isSelected, the cap re-application after prune).

Verification

• New SelectionState unit tests + Robolectric recomposition-isolation test.
• 1,768 existing unit tests pass across the 10 touched modules; full FOSS debug build green.
• Codex plan review + implementation review (the cap-after-prune fix came from the impl review).
• On-device Pixel 7a: multi-select + select-all + clear on Deduplicator/AppControl/AppCleaner/SystemCleaner, keep-one cap holds, 0 crashes/ANRs.