perf(build): use all cores in host builds — wx lib, test apps, gal-webgl

env.sh exports a docker-safe JOBS=1 default, and every host build silently
inherited it (the docker kicad path dodges it by passing -j explicitly):

- build-wx-wasm.sh: the intended "${JOBS:-nproc}" fallback sat BELOW the
  env.sh source, so it was dead code — full wx builds ran make -j1 on the
  Mac and on CI. Compute the all-cores default before env.sh instead
  (explicit JOBS/PARALLEL_JOBS still wins); also -j the PCRE pre-build.
- build-wasm-test.sh: same default fix, plus fan the post-link
  hoist+asyncify loop out across JOBS with xargs -P. Per-app wasm-opt
  can't feed many cores (small modules), so serial stays ~4min even with
  BINARYEN_CORES=16; fanning across the 74 independent apps is what
  scales. Safe: apply-asyncify is in-place per wasm, injector tmp is
  per-js, HOIST_WASMOPT resolved once up front.
- build-gal-webgl-test.sh: make had no -j at all.

Measured on a 16-core M4 Max, clean test-app build: 15m36s (-j1) → 2m08s,
peak RAM 10.7 GB summed across all build processes (64 GB machine; CI
runners have 120 GB). Core counts are always derived from nproc at
runtime — nothing hardcoded, CI workers differ.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XeiSRRScdaox5jBueJNcyG

scripts/build-gal-webgl-test.sh

@@ -21,6 +21,10 @@ set -e
 
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 
+# Default to all cores BEFORE env.sh (its docker-safe JOBS=1 default would stick
+# otherwise); an explicit JOBS/PARALLEL_JOBS from the caller still wins.
+JOBS="${JOBS:-$(nproc 2>/dev/null || sysctl -n hw.ncpu 2>/dev/null || echo 4)}"
+
 # Source common environment (sets up local emsdk)
 QUIET=1 source "$SCRIPT_DIR/common/env.sh"
 
@@ -76,9 +80,9 @@ python3 generate_shaders.py
 echo ""
 echo "Building..."
 if [ "$DEBUG_BUILD" = "1" ]; then
-    make DEBUG=1
+    make -j"${JOBS:-1}" DEBUG=1
 else
-    make
+    make -j"${JOBS:-1}"
 fi
 
 echo ""