lang: catch/onfail error bindings take parens

try foo() catch (e) { }   // legal
try foo() catch e { }     // parse error with a migration hint

Same capture style as the for-loop. All four catch shapes keep working
with the parenthesized binding — block, bare-expression body, and the
== match sugar — and the no-binding forms are unchanged. onfail follows
the same rule (onfail (e) { }); its expression-cleanup form is
disambiguated by the paren-group-before-brace lookahead, so
onfail (f()); stays an expression cleanup.

AST unchanged; the printer renders the parens; the #run escape help
text updated. Corpus migrated (57 catch + 3 onfail bindings, in-source
parser test strings, specs incl. grammar rules, readme untouched —
no catch examples there).

Regression: examples/1157-diagnostics-catch-binding-needs-parens.sx;
re-captured stderr for 1010/1013/1037/1123 (migrated source echoed in
carets + help text).

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

@@ -13,7 +13,7 @@ wrap :: ($T: Type, f: Closure() -> (T, !E)) -> (T, !E) { return try f(); }
 
 main :: () -> s32 {
     // success, consumed by catch
-    print("catch={}\n", wrap(s32, closure(() -> (s32, !E) { return 7; })) catch e -1);   // 7
+    print("catch={}\n", wrap(s32, closure(() -> (s32, !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)
@@ -21,9 +21,9 @@ main :: () -> s32 {
     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(s32, closure(() -> (s32, !E) { raise error.Bad; }) ) catch e -1); // -1
+    print("fail={}\n", wrap(s32, closure(() -> (s32, !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
+    print("u8={}\n", wrap(u8, closure(() -> (u8, !E) { return 200; })) catch (e) 0);         // 200
     return 0;
 }