fix: suppress stdout log spam when daemon is already running

[kianwoon]

Summary

• Add alreadyRunning flag to DaemonStartResult — set when startDaemon() detects the daemon is already running
• CLI handler (index.ts) now suppresses all output when alreadyRunning is true, exiting silently with code 0
• Eliminates the 32K+ "already running" messages that accumulate in stdout.log from launchd KeepAlive re-invocations

Test plan

• TypeScript compiles cleanly (npx tsc --noEmit)
• All 22 daemon tests pass
• node dist/index.js start when already running produces no output, exits 0
• node dist/index.js reload still works normally
• Build succeeds (npm run build)

Closes #217