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/0756-modules-same-name-alias-per-source/a.sx

@@ -0,0 +1,4 @@
+// Module A aliases `Id` to `i32`. A bare `Id` in this module resolves to A's
+// alias regardless of B's same-name alias (per-source alias visibility).
+Id :: i32;
+a_val :: () -> i64 { x : Id = 100; y : i64 = xx x; return y; }

examples/modules/0756-modules-same-name-alias-per-source/b.sx

@@ -0,0 +1,5 @@
+// Module B aliases the SAME name `Id` to a DIFFERENT type `f64`. A bare `Id` in
+// this module resolves to B's `f64` alias, not A's `i32` — each module's alias
+// is keyed to its own source, so the two never collide last-wins.
+Id :: f64;
+b_val :: () -> f64 { x : Id = 2; return x + 0.5; }