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.
Cross-module example (main → b → c) referencing c's lib-less C imports
transitively. The non-transitive C-import gate (lower/decl.zig
c_import_bare) must police the legacy `#foreign` form and the new
`extern` keyword IDENTICALLY — same 'C function not visible' diagnostic,
not the generic top-level-name wording. Today the extern twin escapes the
c_import_bare gate (body is an empty block, not foreign_expr) and is only
caught by the general isNameVisible gate, yielding the generic message.
Expected snapshot pins the DESIRED equivalent wording; the next commit
aligns the gate to green it. Prerequisite for migrating the fn-decl
`#foreign` path onto `extern`.
443/444 corpus (1228 xfail), 444 unit.
