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/basic/0034-basic-string-comparison.sx

@@ -0,0 +1,23 @@
+#import "modules/std.sx";
+#import "modules/math";
+#import "modules/build.sx";
+#import "modules/std/test.sx";
+pkg :: #import "tests/fixtures/testpkg";
+
+main :: () {
+
+    // ========================================================
+    // 24. STRING COMPARISON
+    // ========================================================
+    print("=== 24. String Comparison ===\n");
+    {
+        a := "hello";
+        b := "hello";
+        c := "world";
+        print("str-eq: {}\n", a == b);
+        print("str-neq: {}\n", a != c);
+        print("str-diff: {}\n", a == c);
+        empty := "";
+        print("empty-eq: {}\n", empty == "");
+    }
+}