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/1168-diagnostics-generic-param-uninferrable.sx

@@ -0,0 +1,19 @@
+// A direct call to a generic fn whose arguments cannot bind a TYPE
+// param diagnoses at the call site instead of monomorphizing with the
+// param unbound. A `string` arg at a `[]$T` param is the canonical
+// uninferrable shape (string deliberately does not bind `[]$T`); it
+// used to stamp `.unresolved` through the body and PANIC the compiler
+// at LLVM emission via the sentinel tripwire.
+//
+// Regression (issue 0126, diagnostic half).
+
+#import "modules/std.sx";
+
+first :: (xs: []$T) -> T {
+    return xs[0];
+}
+
+main :: () -> i32 {
+    print("{}\n", first("abc"));
+    return 0;
+}