issues/0065: RESOLVED — value-block destructure parses

The block-value rework routes value-position `{ … }` through the same
statement parser as every other block, so a destructure decl (and any
statement form) inside a value-bound block now parses, with the trailing
expression as the block's value. The `defer { … }` half was fixed
earlier (634cf9b). Regression: examples/0042-basic-block-value-destructure.sx.

Gates: zig build test, run_examples.sh -> 344 passed.

examples/0042-basic-block-value-destructure.sx

@@ -0,0 +1,25 @@
+// A value-position block (`x := { … }`, a call argument, …) parses any
+// statement form in its body — including a destructure decl — and yields its
+// trailing expression as the value. Previously a braced value block routed
+// through a restricted expression parser that rejected destructures with
+// "expected ';'".
+//
+// Regression (issue 0065).
+
+#import "modules/std.sx";
+
+pair :: () -> (s32, s32) { (5, 7) }
+
+main :: () -> s32 {
+    // destructure decl inside a value-bound block
+    sum := {
+        a, b := pair();
+        a + b               // trailing expression → the block's value
+    };
+    print("sum: {}\n", sum);          // 12
+
+    // block expression directly as a call argument
+    print("sq: {}\n", { x := 4; x * x });   // 16
+
+    sum
+}

examples/expected/0042-basic-block-value-destructure.exit

@@ -0,0 +1 @@
+12

examples/expected/0042-basic-block-value-destructure.stderr

@@ -0,0 +1 @@
+

examples/expected/0042-basic-block-value-destructure.stdout

@@ -0,0 +1,2 @@
+sum: 12
+sq: 16

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

@@ -1,14 +1,14 @@
 # 0065 — block-expression body does not parse a destructure decl (`v, e := f();`)
 
-> **PARTIALLY RESOLVED (defer manifestation, this session).** A braced
+> **RESOLVED.** Two fixes landed:
-> `defer { … }` body now parses via `parseBlock` (src/parser.zig, the
+> - The braced `defer { … }` body now parses via `parseBlock` (src/parser.zig,
-> `kw_defer` arm) instead of `parseExpr`, mirroring `onfail`. So
+>   the `kw_defer` arm) instead of `parseExpr`, mirroring `onfail`. Regression:
-> `defer { v, e := f(); … }`, `defer { x() catch e … }`, and plain
+>   `examples/1050-errors-defer-block-body.sx` (commit `634cf9b`).
-> `defer { stmt; }` all parse and run. Regression:
+> - The general *value-producing block in binding position* fell out of the
-> `examples/1050-errors-defer-block-body.sx`. **Still open:** the
+>   trailing-`;` block-value rework: value-position `{ … }` now routes through
-> general *value-producing block in binding position*
+>   the same statement parser as every other block, so a destructure decl (and
-> (`y := { v, e := f(); v };`) — a distinct parser path — does not parse
+>   any statement form) parses, and the trailing expression is the block's
-> a destructure decl; see the second reproduction below.
+>   value. Regression: `examples/0042-basic-block-value-destructure.sx`.
 
 ## Symptom