feat(#218)!: complete Rust-like record migration — 257/257 green

Migrated the remaining expression-position record literals to #{ }
(compiler-as-oracle, iterated to green):
- test/e2e/fixtures/counter.affine (tea_run arg record)
- test/e2e/fixtures/full_pipeline.affine (fn-return + Rect(#{}) arg)
- test/e2e/fixtures/titlescreen.affine (title_init body + 4 match-arm
  records + tea_run arg)
- examples/comprehensive_test.affine (fn-return + Rect(#{}) arg)
- stdlib/testing.affine (benchmark-result record — the ONE stdlib
  record literal; earlier survey missed it, parse-gated)

Type-position records, struct/type declarations, blocks, and match-arm
blocks left unchanged (different grammar rules — verified).

Full dune gate now GREEN: 257/257, 0 failures. Conflicts 72->68 S/R,
10->7 R/R (residual families tracked on #215). Breaking syntax change
— review-gated, do not auto-merge.

Refs #218 #215

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

examples/comprehensive_test.affine

@@ -12,7 +12,7 @@ enum Shape {
 }
 
 fn vec2_add(a: Vec2, b: Vec2) -> Vec2 {
-  { x: a.x + b.x, y: a.y + b.y }
+  #{ x: a.x + b.x, y: a.y + b.y }
 }
 
 fn area(s: Shape) -> Int {
@@ -30,7 +30,7 @@ fn larger_area(s1: Shape, s2: Shape) -> Int = max(area(s1), area(s2));
 
 fn main() -> () {
   let circle = Circle(5);
-  let rect = Rect({ x: 3, y: 4 });
+  let rect = Rect(#{ x: 3, y: 4 });
   let result = larger_area(circle, rect);
   ();
 }

stdlib/testing.affine

@@ -303,7 +303,7 @@ fn bench(f: () -> (), iterations: Int) -> BenchResult {
   }
 
   let tot = time_now() - start;
-  {
+  #{
     iterations: iterations,
     total_time: tot,
     avg_time: tot / float(iterations)

test/e2e/fixtures/counter.affine

@@ -68,7 +68,7 @@ fn counter_subs(model: Int) -> String {
 // Wire up the TEA runtime and hand off to the interpreter loop.
 
 fn main() -> () {
-  tea_run({
+  tea_run(#{
     init:          counter_init,
     update:        counter_update,
     view:          counter_view,

test/e2e/fixtures/full_pipeline.affine

@@ -13,7 +13,7 @@ enum Shape {
 }
 
 fn vec2_add(a: Vec2, b: Vec2) -> Vec2 {
-  { x: a.x + b.x, y: a.y + b.y }
+  #{ x: a.x + b.x, y: a.y + b.y }
 }
 
 fn area(s: Shape) -> Int {
@@ -31,7 +31,7 @@ fn larger_area(s1: Shape, s2: Shape) -> Int = max(area(s1), area(s2));
 
 fn main() -> () {
   let circle = Circle(5);
-  let rect = Rect({ x: 3, y: 4 });
+  let rect = Rect(#{ x: 3, y: 4 });
   let result = larger_area(circle, rect);
   ();
 }

test/e2e/fixtures/titlescreen.affine

@@ -44,7 +44,7 @@ struct TitleModel {
 // ── init ─────────────────────────────────────────────────────────────────────
 
 fn title_init() -> TitleModel {
-  {
+  #{
     screen_w:    1280,
     screen_h:    720,
     bgm_playing: 0,
@@ -58,10 +58,10 @@ fn title_init() -> TitleModel {
 
 fn title_update(msg: TitleMsg, model: TitleModel) -> TitleModel {
   match msg {
-    NewGame  => { screen_w: model.screen_w, screen_h: model.screen_h, bgm_playing: model.bgm_playing, selected: "new_game" },
-    LoadGame => { screen_w: model.screen_w, screen_h: model.screen_h, bgm_playing: model.bgm_playing, selected: "load_game" },
-    Settings => { screen_w: model.screen_w, screen_h: model.screen_h, bgm_playing: model.bgm_playing, selected: "settings" },
-    Credits  => { screen_w: model.screen_w, screen_h: model.screen_h, bgm_playing: model.bgm_playing, selected: "credits" }
+    NewGame  => #{ screen_w: model.screen_w, screen_h: model.screen_h, bgm_playing: model.bgm_playing, selected: "new_game" },
+    LoadGame => #{ screen_w: model.screen_w, screen_h: model.screen_h, bgm_playing: model.bgm_playing, selected: "load_game" },
+    Settings => #{ screen_w: model.screen_w, screen_h: model.screen_h, bgm_playing: model.bgm_playing, selected: "settings" },
+    Credits  => #{ screen_w: model.screen_w, screen_h: model.screen_h, bgm_playing: model.bgm_playing, selected: "credits" }
   }
 }
 
@@ -84,7 +84,7 @@ fn title_subs(model: TitleModel) -> String {
 // ── main ──────────────────────────────────────────────────────────────────────
 
 fn main() -> () {
-  tea_run({
+  tea_run(#{
     init:          title_init,
     update:        title_update,
     view:          title_view,