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>

daemon/com.user.claude-usage-daemon.plist

@@ -0,0 +1,43 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+    <key>Label</key>
+    <string>com.user.claude-usage-daemon</string>
+
+    <key>ProgramArguments</key>
+    <array>
+        <string>__PYTHON_BIN__</string>
+        <string>__DAEMON_PATH__</string>
+    </array>
+
+    <key>WorkingDirectory</key>
+    <string>__REPO_DIR__</string>
+
+    <key>RunAtLoad</key>
+    <true/>
+
+    <key>KeepAlive</key>
+    <dict>
+        <key>SuccessfulExit</key>
+        <false/>
+    </dict>
+
+    <key>ThrottleInterval</key>
+    <integer>10</integer>
+
+    <key>StandardOutPath</key>
+    <string>__LOG_OUT__</string>
+
+    <key>StandardErrorPath</key>
+    <string>__LOG_ERR__</string>
+
+    <key>EnvironmentVariables</key>
+    <dict>
+        <key>HOME</key>
+        <string>__HOME__</string>
+        <key>PATH</key>
+        <string>/usr/local/bin:/opt/homebrew/bin:/usr/bin:/bin</string>
+    </dict>
+</dict>
+</plist>