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.
Two flat imports each declare `absval` via `extern libc "abs"` (the
`extern` twin of example 0729's `#foreign` form). Like its #foreign twin,
this must compile + run (prints 7), not error as an ambiguous bare-call
collision.
Today `isPlainFreeFn` / `isPlainFreeFnDecl` exclude a `#foreign` body but
classify an empty-block `extern` fn as a plain free function, so the two
extern authors ARE counted in the bare-call ambiguity verdict and the call
errors. A third extern/#foreign divergence (after visibility + variadic)
and a prerequisite for migrating the fn-decl `#foreign` path onto `extern`.
646 corpus (1230 xfail), 444 unit.
