feat: separate bulk-edit trigger from column sort

[mylaser215]

Summary

Follow-up to #787. Improves the bulk edit UX in MDM fileclass table views:

• Separate bulk-edit from sort: Column header click now only sorts. A dedicated pencil icon button triggers bulk edit for each column, preventing accidental edits when sorting.
• Checkbox toggle isolation: The checkbox toggler (list-todo icon) uses stopPropagation() to avoid triggering column sort when toggling row selection.
• Pencil buttons auto-show/hide: Bulk-apply pencil buttons appear only when checkboxes are visible, keeping the UI clean.
• Async safety for bulk edit confirm: MultiTargetModificationConfirmModal confirm handler now uses async/await to process files sequentially, preventing potential race conditions when editing multiple files.
• CSS cleanup: Unified icon sizes (22px), added hover styles for bulk-apply buttons, added cleanTable cleanup for .bulk-apply-btn elements.

Files Changed

• src/fileClass/views/tableViewComponents/fileClassDataviewTable.ts — UI logic refactor
• src/assets/css/fileclass.scss — Styles for .bulk-apply-btn and .checkbox-toggler
• src/fields/base/BaseModal.ts — async/await in confirm handler

Test plan

• Open a fileclass table view with multiple fields
• Click column headers → should only sort (no bulk edit modal)
• Toggle checkboxes → pencil icons appear on each column
• Click pencil icon → bulk edit modal opens for that column
• Hide checkboxes → pencil icons disappear
• Bulk edit multiple files → verify no race conditions (fields not cleared)

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