fix(fls): archive path folding measured against Swift

41 path pairs replayed in the Swift core decide which spellings name
the same file. Two corrections: full Unicode case folding (ß, ligatures,
final sigma, micro, long s) instead of toLowerCase, and width folding of
the whole Halfwidth and Fullwidth Forms block. Swift treats composed and
decomposed spellings as one dictionary key; here the writer refuses both.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/swift-oracle/run.sh

@@ -11,4 +11,5 @@ docker run --rm -v "$root:/work" -w /work/tools/swift-oracle swift:6.1-jammy sh
     set -e
     swift build -q
     .build/debug/Oracle /work/packages/core/test/scenarios
-    .build/debug/Oracle --corpus /work/corpus /work/corpus/corpus.swift.json'
+    .build/debug/Oracle --corpus /work/corpus /work/corpus/corpus.swift.json
+    .build/debug/Oracle --path-folding /work/packages/fls/test/path-folding.cases.json /work/packages/fls/test/path-folding.swift.json'