TableView sweep batch 3: last three sorting grids + retire the DataGrid package

[niksedk]

Final batch of the TableView migration (#13017, #13018, #13019). Zero DataGrids remain; the Avalonia.Controls.DataGrid package is gone from the build.

Conversions (sorting kept via TableViewHeaderSorter)

• Shortcuts — all five columns sortable (ActiveIn, group, category, name, shortcut); widths measured from actual content at construction; header double-click sorts instead of opening the detect-key dialog. Note: a search/filter change rebuilds the list in default order (the DataGrid's view-sort survived refilters).
• BatchConvert — file grid sortable by name/format/status and by raw byte size (better than the old string sort). Found + fixed a pre-existing hazard: the conversion loop enumerated the live ObservableCollection from a background task (a mid-run filter change could throw); it now snapshots the job list, which also makes mid-run sorting safe. The functions checklist keeps fixed order and now shows headers (TableView can't hide them).
• FixCommonErrors — rules and fixes grids fully sortable. Rule execution order is now decoupled from display order (ApplyFixes runs selected rules in canonical order), so a cosmetic sort can never change fix results — under the DataGrid this held only because sorting was view-level.

Sorter perf fix

Headless benchmarking (10k rows) showed SelectedItems.Add is O(n) per call on ListBox-based controls (8.6 s for 2,000 adds) while a batched SelectRange is ~4 ms. The sorter now refills the collection detached and restores selection through the selection model by index.

For the record, DataGrid vs TableView on identical 10k-row data: first layout 378 → 44 ms, ItemsSource reset ×10 480 → 64 ms, scroll jumps comparable.

DataGrid retirement

• Package reference, theme include, and both behavior classes (DataGridScrollBarBehavior, DataGridCheckboxMultiSelect) deleted; DataGrid styles stripped from UiTheme/Styles.axaml; DataGrid cell themes and helpers removed from UiUtil.
• Grid-lines setting enum is now SE-owned (SeGridLinesVisibility, same member names — persisted settings keep working).
• The TableView header background resource the DataGrid theme used to supply is now defined in Styles.axaml with the same value.

Testing

Full solution builds clean; all 983 UI tests pass (one obsolete trough-paging test removed with its subject). Smoke-test priorities:

• Shortcuts: sort each column, edit a shortcut after sorting, search-filter reset
• BatchConvert: sort by size, run a batch, sort mid-run, filter mid-run
• FixCommonErrors: sort rules then verify fix results are unchanged; sort fixes and apply a subset
• Theme check (default + custom): grid headers still have their background everywhere
• macOS "Show scroll bars: Always" still gives expanded scrollbars (the DataGrid-specific workaround was removed; ListBox path remains)

🤖 Generated with Claude Code