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/platform/expected/1646-platform-asm-value-binding.ir

@@ -0,0 +1,11 @@
+
+; Function Attrs: nounwind
+define i32 @main() #0 {
+entry:
+  %asm = call i64 asm "mov ${0}, #99", "=r"()
+  %alloca = alloca i64, align 8
+  store i64 %asm, ptr %alloca, align 8
+  %load = load i64, ptr %alloca, align 8
+  %ca.tr = trunc i64 %load to i32
+  ret i32 %ca.tr
+}