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/0782-modules-bare-generic-instance-ambiguous-authors/p.sx

@@ -0,0 +1,9 @@
+// Author P's generic `Box` — one i64 field. Flat-imported alongside q.sx's
+// same-name `Box`, so a bare `Box` reference is ambiguous.
+Box :: struct($T: Type) {
+    x: T;
+
+    make :: (value: T) -> Box(T) {
+        .{ x = value }
+    }
+}

examples/modules/0782-modules-bare-generic-instance-ambiguous-authors/q.sx

@@ -0,0 +1,10 @@
+// Author Q's generic `Box` — two i64 fields. Flat-imported alongside p.sx's
+// same-name `Box`, so a bare `Box` reference is ambiguous.
+Box :: struct($T: Type) {
+    x: T;
+    y: T;
+
+    make :: (value: T) -> Box(T) {
+        .{ x = value, y = value }
+    }
+}