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/0048-basic-for-array-large.sx

@@ -0,0 +1,24 @@
+// Collection-form `for` over an array, by-value capture: each iteration
+// reads ONE element from the array's storage (GEP + load), and the capture
+// stays a copy — mutating it never writes back to the array.
+// Regression (issue 0110): the element fetch was `index_get` on the array
+// VALUE, spilling a full copy of the array to a stack temp per iteration —
+// O(N²) bytes copied, and (pre-0109) per-iteration stack growth that made
+// this 4096-element loop segfault.
+
+#import "modules/std.sx";
+
+main :: () -> i32 {
+    arr : [4096]i64 = ---;
+    i := 0;
+    while i < 4096 { arr[i] = i; i += 1; }
+    sum := 0;
+    for arr (x) { sum += x; }
+    print("sum={}\n", sum);
+
+    // By-value capture is a copy: mutating it leaves the array untouched.
+    small : [3]i64 = .[10, 20, 30];
+    for small (x) { x += 100; }
+    print("copy-guard: {} {} {}\n", small[0], small[1], small[2]);
+    0
+}