fix(parser): parse braced defer { … } body as a statement block (issue 0065)

A braced `defer` body routed through `parseExpr` + a mandatory trailing
`;`, so it parsed the `{ … }` as a block-EXPRESSION whose statement loop
doesn't handle a destructure decl or a `catch`-statement — `defer { v, e
:= f(); … }` and `defer { x() catch e … }` failed with "expected ';'",
and even `defer { stmt; }` needed a spurious trailing semicolon.

Now the `kw_defer` arm parses a braced body with `parseBlock` (the same
path `onfail` uses), so every statement form works; the bare-expression
form (`defer expr;`) is unchanged. `in_defer_body` is still set before
parsing, so the cleanup-body control-flow bans (return/break/continue/
try/raise) and the E1.7 failable-absorption check still fire.

Resolves the `defer` manifestation of issue 0065 (the general
value-block-in-binding-position destructure remains open). Regression:
examples/1050-errors-defer-block-body.sx.

Gates: zig build, zig build test, run_examples.sh -> 341 passed, 0 failed.

issues/0065-block-expr-destructure-decl-parse.md

@@ -1,5 +1,15 @@
 # 0065 — block-expression body does not parse a destructure decl (`v, e := f();`)
 
+> **PARTIALLY RESOLVED (defer manifestation, this session).** A braced
+> `defer { … }` body now parses via `parseBlock` (src/parser.zig, the
+> `kw_defer` arm) instead of `parseExpr`, mirroring `onfail`. So
+> `defer { v, e := f(); … }`, `defer { x() catch e … }`, and plain
+> `defer { stmt; }` all parse and run. Regression:
+> `examples/1050-errors-defer-block-body.sx`. **Still open:** the
+> general *value-producing block in binding position*
+> (`y := { v, e := f(); v };`) — a distinct parser path — does not parse
+> a destructure decl; see the second reproduction below.
+
 ## Symptom
 
 A destructure declaration (`v, e := f();`) inside a **block used in