fix+feat(BinaryAnalysis): OUTDATED false-positive + Diff panel redesign

BUG fix — OUTDATED badge on first HexEditor click:
  OnHexEditorSelectionChanged no longer sets IsOutdated=true. Caret movement
  does not make a scan stale; only OnFileChanged (FileSystemWatcher) should.
  This eliminated the spurious OUTDATED on every first click after a scan.

Diff panel — Swap A↔B:
  '⇄' button in snapshot bar swaps both combos without triggering a double diff
  (SelectionChanged unsubscribed during swap, re-subscribed after).

Diff panel — Export CSV:
  '↓ CSV' toolbar button + context menu 'Export visible rows to CSV…'.
  Exports only the currently filtered/visible rows; SaveFileDialog with
  datestamped default filename; RFC-4180 quoting via CsvEscape.

Diff panel — Enter key → GoToOffset:
  DataGrid.KeyDown handler: Enter on selected row calls vm.NavigateToOffset.

Diff panel — Column sort:
  DataGrid.Sorting event + DiffEntryComparer (IComparer); supports Status,
  Offset, Value, Encoding, OldValue columns. Single-column sort with
  Ascending/Descending toggle; sort arrow shown on active column.

Diff panel — Theme / foreground:
  DataGridRow.Foreground = TE_Foreground (DynamicResource) so text is readable
  in both Dark and Light themes. Cell TextBlocks SetResourceReference to
  TE_Foreground. Search bar uses TE_Background/TE_Foreground.

Diff panel — Text search bar:
  New row between filter chips and DataGrid: 🔍 TextBox + ✕ clear button.
  Predicate matches Value, OldValue, Offset (hex), Encoding — case-insensitive.
  Applied as an extra predicate on the same CollectionView (no re-diff).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: abbaye