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/1645-platform-asm-aarch64-add.ir

@@ -0,0 +1,21 @@
+
+; Function Attrs: nounwind
+define internal i64 @add_asm(i64 %0, i64 %1) #0 {
+entry:
+  %alloca = alloca i64, align 8
+  store i64 %0, ptr %alloca, align 8
+  %allocaN = alloca i64, align 8
+  store i64 %1, ptr %allocaN, align 8
+  %load = load i64, ptr %alloca, align 8
+  %loadN = load i64, ptr %allocaN, align 8
+  %asm = call i64 asm "add ${0}, ${1}, ${2}", "=r,r,r"(i64 %load, i64 %loadN)
+  ret i64 %asm
+}
+
+; Function Attrs: nounwind
+define i32 @main() #0 {
+entry:
+  %call = call i64 @add_asm(i64 40, i64 2)
+  %ca.tr = trunc i64 %call to i32
+  ret i32 %ca.tr
+}