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/ffi/1210-ffi-02-small-struct.h

@@ -0,0 +1,29 @@
+// FFI struct-marshalling baselines covering four aggregate ABI slots:
+//   Vec2   — 8 B,  two f32         — register-pair (float) path
+//   Vec4f  — 16 B, four f32        — HFA (homogeneous float aggregate)
+//   Pair64 — 16 B, two i64         — 9..16 B int ABI ([2 x i64] coercion)
+//   Quad32 — 16 B, four i32        — 9..16 B int ABI ([2 x i64] coercion)
+// Declared here so the .c has a header to include; sx side imports
+// via `#source` only and re-declares the structs natively (c_import
+// rewrites struct-typed params/returns to *void).
+
+typedef struct { float x; float y; }                           Vec2;
+typedef struct { float x; float y; float z; float w; }         Vec4f;
+typedef struct { long long a; long long b; }                   Pair64;
+typedef struct { int a; int b; int c; int d; }                 Quad32;
+
+Vec2      ffi_vec2_make    (float x, float y);
+Vec2      ffi_vec2_swap    (Vec2 v);
+float     ffi_vec2_sum     (Vec2 v);
+
+Vec4f     ffi_vec4f_make   (float x, float y, float z, float w);
+Vec4f     ffi_vec4f_reverse(Vec4f v);
+float     ffi_vec4f_sum    (Vec4f v);
+
+Pair64    ffi_pair64_make  (long long a, long long b);
+Pair64    ffi_pair64_swap  (Pair64 p);
+long long ffi_pair64_sum   (Pair64 p);
+
+Quad32    ffi_quad32_make  (int a, int b, int c, int d);
+Quad32    ffi_quad32_reverse(Quad32 q);
+int       ffi_quad32_sum   (Quad32 q);