Add macOS host support

Cherry-picks the macOS-specific pieces from PR #5: Python daemon using
bleak (CoreBluetooth backend), LaunchAgent template, flash-mac.sh, and
install-mac.sh. Token is read from the macOS Keychain ("Claude
Code-credentials" service); Linux behavior is unchanged. README split
into "macOS installation" and "Linux installation" sections with
parallel Flash / Pair / Install subsections.

Co-Authored-By: Chris Davidson <36679917+lorddavidson@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

flash-mac.sh

@@ -0,0 +1,34 @@
+#!/bin/bash
+# Build and flash Clawdmeter firmware on macOS.
+# Usage:
+#   ./flash-mac.sh                       # auto-detect /dev/cu.usbmodem*
+#   ./flash-mac.sh /dev/cu.usbmodem1101  # explicit USB serial port
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+PORT="$1"
+
+if [ -z "$PORT" ]; then
+    PORT=$(ls /dev/cu.usbmodem* 2>/dev/null | head -1)
+    if [ -z "$PORT" ]; then
+        echo "Error: no /dev/cu.usbmodem* device found. Plug in via USB-C."
+        exit 1
+    fi
+fi
+
+if ! command -v pio >/dev/null; then
+    echo "Error: 'pio' not found. Install with:"
+    echo "  brew install platformio"
+    exit 1
+fi
+
+echo "=== Flashing Clawdmeter ==="
+echo "Port: $PORT"
+echo ""
+
+cd "$SCRIPT_DIR/firmware"
+pio run -t upload --upload-port "$PORT"
+
+echo ""
+echo "=== Done ==="
+echo "Monitor with: pio device monitor -p $PORT -b 115200"