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/errors/expected/1056-errors-enum-value-failable-tuple-and-comptime.stdout

@@ -0,0 +1,13 @@
+F1 ok: err int = 0
+F1 ok bare-if: ok
+F1 ok guard: c = 2
+F1 bad: err nonzero = true
+F1 bad: is Nope (ok)
+F1 bad: tag name = Nope
+F2 red: err int = 0
+F2 red bare-if: ok
+F2 red != Nope (ok)
+F2 red guard: c = 0
+F2 blue: err int = 0, c = 2
+F2 err: err nonzero = true
+F2 err: is Nope (ok)