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/diagnostics/1107-diagnostics-ref-capture-value-arg-diagnostic.sx

@@ -0,0 +1,18 @@
+// A by-reference loop capture (`for xs (*m)`) binds `m` to a `*T`.
+// Passing it where a `T` value is expected used to slip through to the
+// LLVM verifier ("Call parameter type does not match function signature").
+// The compiler now reports it at the call site with a fix-it: write `m.*`.
+
+#import "modules/std.sx";
+
+Move :: struct { flag: i64; }
+
+take :: (m: Move) -> i64 { return m.flag; }
+
+main :: () -> i32 {
+    moves : [2]Move = .[ Move.{ flag = 1 }, Move.{ flag = 2 } ];
+    for moves (*m) {
+        take(m);
+    }
+    return 0;
+}