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/1043-errors-lambda-raise-annotation-hint.sx

@@ -9,7 +9,7 @@
 
 E :: error { Neg }
 
-take :: (cb: Closure(s32) -> (s32, !E), x: s32) -> s32 { return cb(x) catch e -1; }
+take :: (cb: Closure(s32) -> (s32, !E), x: s32) -> s32 { return cb(x) catch (e) -1; }
 
 main :: () -> s32 {
     // `-> s32` (non-failable) but the body raises → lambda-specific hint: