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/0813-modules-same-name-error-set-lambda-own-wins.sx

@@ -21,7 +21,7 @@ IoErr :: error { Disk }
 
 main :: () -> s32 {
     fail_own := closure(() -> !IoErr { raise error.Disk; });
-    fail_own() catch e {
+    fail_own() catch (e) {
         if e == error.Disk { print("own=Disk\n"); }
     };
     d := dep_err();