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/0778-modules-bare-generic-instance-by-value-receiver/b.sx

@@ -0,0 +1,16 @@
+// The bare-VISIBLE author: a one-field generic `Box` (size 8) with a BY-VALUE
+// receiver method `dbl` (`self: Box`). `b.sx` flat-imports `c.sx`, so a file
+// importing only b.sx reaches `c.Box` at two hops and must NOT dispatch to it.
+Box :: struct($T: Type) {
+    x: T;
+
+    make :: (value: T) -> Box(T) {
+        .{ x = value }
+    }
+
+    dbl :: (self: Box) -> T {
+        self.x * 2
+    }
+}
+
+#import "c.sx";