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/0833-modules-namespace-alias-carried-collision-ambiguous/a.sx

@@ -0,0 +1,2 @@
+t :: #import "x.sx";
+use_a :: () -> i64 { t.fx() }

examples/modules/0833-modules-namespace-alias-carried-collision-ambiguous/b.sx

@@ -0,0 +1,2 @@
+t :: #import "y.sx";
+use_b :: () -> i64 { t.fy() }

examples/modules/0833-modules-namespace-alias-carried-collision-ambiguous/x.sx

@@ -0,0 +1 @@
+fx :: () -> i64 { 1 }

examples/modules/0833-modules-namespace-alias-carried-collision-ambiguous/y.sx

@@ -0,0 +1 @@
+fy :: () -> i64 { 2 }