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/errors/1044-errors-generic-failable-composition.sx

@@ -0,0 +1,29 @@
+// Generic function with a value-carrying `!` return composes (ERR E5.1
+// sub-feature 8). A `$T: Type` generic whose return is `(T, !E)` monomorphizes
+// per call: `return try f()` propagates the closure's error, and each
+// monomorphization's success value flows through as the concrete `T`.
+// (Regression: confirms issue 0062 was an invalid-syntax repro — the bug only
+// appeared with the non-generic `T: Type` form; the `$T` form works.)
+
+#import "modules/std.sx";
+
+E :: error { Bad }
+
+wrap :: ($T: Type, f: Closure() -> (T, !E)) -> (T, !E) { return try f(); }
+
+main :: () -> i32 {
+    // success, consumed by catch
+    print("catch={}\n", wrap(i32, closure(() -> (i32, !E) { return 7; })) catch (e) -1);   // 7
+
+    // success, consumed by destructure (binds value + error slot); the value
+    // slot is read only under an `if !err` guard (ERR E1.8 path-sensitivity)
+    r, err := wrap(i32, closure(() -> (i32, !E) { return 9; }));
+    if !err { print("destr={} ok=true\n", r); }                                           // destr=9 ok=true
+
+    // failure path: the raised tag propagates through the generic `try`
+    print("fail={}\n", wrap(i32, closure(() -> (i32, !E) { raise error.Bad; }) ) catch (e) -1); // -1
+
+    // a second monomorphization at a different T
+    print("u8={}\n", wrap(u8, closure(() -> (u8, !E) { return 200; })) catch (e) 0);         // 200
+    return 0;
+}