SPL Meter 0.5.0: the capture tool ships prebuilt, for Apple silicon and Intel

Same move as Timers 1.7.0. The capture tool existed only where the macOS
app build had compiled it, with the module trying swiftc on the booth as a
fallback — NA has been logging "spawn spl-capture ENOENT" since its
catalog install. Under the module guide's rule it now ships built:
bin/spl-capture-macos-arm64 and bin/spl-capture-macos-x86_64, signed with
the Developer ID (hardened runtime, audio-input entitlement), from
native/spl-capture.swift via native/build.sh. captureTool() picks the
binary for this platform; where there is none — Windows, until a Windows
implementation exists — measurement reports itself off in the health line
and the device picker while the module stays mounted. The runtime build
and its "building…" state are gone, and the old top-level binary is no
longer gitignored.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

modules/spl-meter/native/build.sh

@@ -0,0 +1,48 @@
+#!/bin/zsh
+# Build this module's native helper for every macOS architecture it ships —
+#   ../bin/spl-capture-macos-arm64 and ../bin/spl-capture-macos-x86_64 —
+# from spl-capture.swift beside this script. Run it on any Mac with the
+# Xcode command line tools; both architectures cross-compile from either.
+# The binaries are committed: a machine running ProdDash never builds
+# anything (docs/MODULE-GUIDE.md, "Native helpers").
+#
+# Signed with a Developer ID Application certificate when one is installed
+# (override with CODESIGN_IDENTITY) — hardened runtime plus the audio-input
+# entitlement, which a helper that reads a microphone needs under the
+# hardened runtime — and ad-hoc otherwise, which is fine on your own Macs.
+#
+# Windows is not built here: there is no Windows implementation of this
+# tool yet, so on Windows the module reports measurement off.
+set -e -u
+cd "$(dirname "$0")"
+
+NAME="spl-capture"
+DEPLOYMENT_TARGET="13.0"
+
+command -v swiftc >/dev/null || {
+  echo "build.sh: swiftc not found — install the Xcode command line tools: xcode-select --install" >&2
+  exit 1
+}
+
+IDENTITY="${CODESIGN_IDENTITY:-}"
+if [[ -z "$IDENTITY" ]]; then
+  IDENTITY=$(security find-identity -v -p codesigning 2>/dev/null \
+    | awk -F'"' '/Developer ID Application/ {print $2; exit}')
+fi
+if [[ -n "$IDENTITY" ]]; then
+  echo "signing as $IDENTITY"
+  SIGN=(--force --sign "$IDENTITY" --options runtime --timestamp)
+else
+  echo "signing ad-hoc (no Developer ID installed — fine on your own Macs)"
+  SIGN=(--force --sign - --options runtime)
+fi
+
+mkdir -p ../bin
+for ARCH in arm64 x86_64; do
+  OUT="../bin/$NAME-macos-$ARCH"
+  echo "  compiling $OUT"
+  swiftc -O -whole-module-optimization -target "$ARCH-apple-macos$DEPLOYMENT_TARGET" -o "$OUT" "$NAME.swift"
+  codesign "${SIGN[@]}" --entitlements helper.entitlements "$OUT"
+  codesign --verify --strict "$OUT"
+  echo "  built $OUT ($(du -h "$OUT" | awk '{print $1}'))"
+done