[launchd] Sync Claude session state on macOS

Adds a launchd agent that runs the existing claude-save make target
every 30 minutes and at login, so macOS machines commit and push
session state the way the systemd timer does on Linux.

The agent runs through /bin/sh because launchd expands neither ~ nor
$HOME in ProgramArguments, and sets PATH explicitly because agents
inherit no shell environment. The claude target loads it via launchctl
bootstrap on darwin.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Makefile

@@ -45,6 +45,11 @@ claude:
 		systemctl --user daemon-reload && \
 		systemctl --user enable --now claude-save.timer; \
 	fi
+	@if [ $(OS_NAME) = "darwin" ]; then \
+		launchctl bootout gui/$$(id -u)/com.powellc.claude-save 2>/dev/null; \
+		launchctl bootstrap gui/$$(id -u) ~/Library/LaunchAgents/com.powellc.claude-save.plist && \
+		echo "claude: loaded com.powellc.claude-save"; \
+	fi
 
 claude-save:
 	@cd $(CLAUDE_HISTORY_DIR) && \