Fix data-panel misassignment (#424)

* Fix facet sort-array bug by encoding panel order as integers

Vega-Lite has a bug where explicit sort arrays on facet field definitions
cause data-panel misalignment. Work around this by
converting discrete facet column values to integer sort indices in the
unified dataset and reconstructing display labels via header.labelExpr.

- Split apply_facet_ordering into resolve_facet_ordering (pure: scale →
  index map) and apply_facet_ordering (rewrites data column to integers)
- Add build_indexed_facet_label_expr to map integers back to labels,
  composing with user RENAMING when present
- Extract apply_binned_facet_reverse for the binned sort: "descending"
  case (unaffected by the bug since it uses a string, not an array)

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

* Deduplicate apply_faceting with apply_facet_aesthetic helper

Extract the per-field facet pipeline (build def, resolve ordering, rewrite
data, label renaming, binned reverse) into apply_facet_aesthetic. Hoist the
shared "move layer/width/height into inner spec" block after the match.

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

* add news bullet

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: teunbrand

CHANGELOG.md

@@ -6,6 +6,7 @@
   separated from directly feeding into the visualisation data (#415)
 - Fixed bug where panel axes were unintentionally anchored to zero when using 
   `FACET ... SETTING free => 'x'/'y'` (#410).
+- Fixed bug where faceted data were matched to the incorrect panels (#409)
 
 ## 0.3.1 - 2026-04-30