perf(web): size-focused wasm-release profile for the canvas build

canvas_bg.wasm shipped at 36.2 MB — plain release (opt-level 3, thin
LTO) piped through wasm-opt -O2. Download size, not throughput, is the
binding constraint for the browser canvas, so solitaire_web now builds
with a dedicated wasm-release profile: opt-level "s", fat LTO, one
codegen unit. Local result: 23.2 MB after the unchanged wasm-opt -O2
pass — 35.9% smaller.

The binaryen pass stays at -O2 (the -Oz grey-screen miscompile note in
build_wasm.sh still applies). profile.strip is deliberately NOT set: on
wasm it also removes the target_features custom section, which makes
wasm-opt reject the module ('all used features should be allowed' on
trunc_sat).

Verified with the new artifact: all 5 play_canvas e2e specs pass (debug
bridge, draw3 param, apply/undo, replay diagnostics, 40-seed autoplay
invariants). Headless pixel verification is inconclusive in this
environment — wgpu cannot create a usable adapter locally and panics
identically on the OLD artifact too — so visual parity should be
confirmed against production after the next deploy.

pkg/ artifacts are intentionally not committed: the web-wasm-rebuild
workflow is the single source of truth and will regenerate them with
this profile on merge.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Cargo.toml

@@ -156,3 +156,19 @@ opt-level = 3
 [profile.release]
 opt-level = 3
 lto = "thin"
+
+# Size-focused profile for the browser canvas build (solitaire_web →
+# canvas_bg.wasm). Download size is the constraint on the web, not peak
+# throughput: fat LTO + one codegen unit + opt-level "s" cut the Bevy wasm
+# bundle substantially versus plain release. This is rustc-side sizing only —
+# the binaryen pass in build_wasm.sh stays at wasm-opt -O2 because -Oz has
+# miscompiled Bevy's render pipeline before (grey screen on first load).
+[profile.wasm-release]
+inherits = "release"
+opt-level = "s"
+lto = "fat"
+codegen-units = 1
+# No `strip`: on wasm it also removes the target_features custom section,
+# which makes wasm-opt reject the module ("all used features should be
+# allowed" on trunc_sat). wasm-opt drops the name section in its output
+# anyway, so strip buys nothing here.