test: group examples into per-category folders

Move examples/*.sx and their expected/ snapshots into per-category
subfolders (examples/<category>/...). Folder = leading filename token,
with ffi-objc/ffi-jni kept whole; filenames are unchanged. The corpus
runner and LSP sweep now discover each category's expected/ dir, while
issues/ stays flat. Example 1058's repo-root-relative companion import
is made file-relative. Path strings embedded in 164 snapshots were
regenerated (path-only changes). Test-layout docs in CLAUDE.md updated.

examples/packs/expected/0545-packs-inline-for-element.stdout

@@ -0,0 +1,11 @@
+bare: 7
+bare: hi
+0: 7
+1: hi
+r0: 1
+r1: two
+10 -> x
+11 -> y
+ran 3
+val: IntBox{v: 42}
+empty ok