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/modules/0729-modules-flat-same-name-extern.sx

@@ -0,0 +1,14 @@
+// fix-0102c (issue 0102) F3 regression: two flat FILE imports each `extern`
+// the SAME libc symbol under the SAME sx name `absval`. The bare-call resolver
+// must NOT count `extern` (non-plain) authors when deciding ambiguity — it
+// filters them out, returns "no rerouting", and the existing first-wins extern
+// dispatch binds the call. A same-name extern collision therefore compiles and
+// runs (master behavior), it does NOT error as ambiguous.
+#import "modules/std.sx";
+#import "0729-modules-flat-same-name-extern/a.sx";
+#import "0729-modules-flat-same-name-extern/b.sx";
+
+main :: () -> i32 {
+    print("absval = {}\n", absval(-7));
+    0
+}